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REESE  LIBRARY 


UNIVERSITY  OF  CALIFORNIA. 
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SEWERAGE. 


THE    DESIGNING,    CONSTRUCTION,    AND 
MAINTENANCE 


OF 


SEWERAGE    SYSTEMS. 


BY 

A.    PRESCOTT    FOLWELL, 

/ » 

Member  American  Society  of  CM  Engineers. 


SECOND   EDITION,  REVISED. 
FIRST    THOUSAND. 


NEW  YORK: 

JOHN   WILEY   &   SONS. 

LONDON:   CHAPMAN  &   HALL,   LIMITED. 

1899. 


Copyright,  1898, 

BY 

A.   PRESCOTT   FOLWELL. 


ROBERT  DRUMMOND,    PRINTER,    NEW  YORK. 


PREFACE. 


For  a  number  of  years  the  author  has  been  looking  for  the 
appearance  of  a  work  on  Sewerage  which  should  embody  the 
most  recent  data  and  ideas  relating  to  the  subject  and  treat 
of  both  the  Combined  and  Separate  Systems  in  a  comprehen- 
sive manner,  recognizing  the  fact  that  such  a  work  is  needed 
by  city  engineers  and  engineering  schools.  None  such  has 
appeared,  and  he  has  consequently  undertaken  the  task  of 
supplying  the  deficiency. 

No  attempt  has  been  made  to  treat  at  length  the  subject 
of  Sewage  Disposal,  for  the  reasons  stated  in  Chapter  II. 
Parts  II  and  III  on  the  Construction  and  Maintenance  of 
Sewers  will,  he  believes,  be  appreciated  by  those  who  are 
called  upon  to  superintend  such  work  without  previous  experi- 
ence, and  even,  he  hopes,  give  valuable  hints  to  many  who 
are  not  novices;  although  he  recognizes  that  the  ground  is  by 
no  means  completely  covered.  For  much  of  the  matter 
therein  contained  he  is  indebted  to  the  engineering  peri- 
odicals, particularly  the  News  and  Record,  but  the  greater  part 
of  it  has  never,  to  his  knowledge,  appeared  in  print. 

While  primarily  intended  for  practising  engineers,  the 
work  has  also  been  arranged  with  the  idea  that  it  may  be 
useful  as  a  text-book  in  engineering  schools;  Part  I  having 
already  been  so  used  by  the  author,  and  Part  II  having  been 
largely  given  in  the  form  of  lectures  to  his  classes. 


PART   I.     DESIGNING. 
CHAPTER  I.    SYSTEM  TO  BE  EMPLOYED. 

ART.  PACK 

1 .  Requirements  of  a  System I 

2.  Dry  Sewage  Methods 2 

3.  Dry  Sewage  Systems 4 

4.  Pneumatic  Systems 7 

5.  Water-carriage  Systems 7 

6.  Combined  and  Separate  Systems 9 

7.  Summary 12 

CHAPTER  II.    SEWAGE  DISPOSAL. 

8.  "  Disposal  "  and  "  Sewage  "  Defined 14 

9.  Aims  of  Disposal 16 

10.  Principles  Involved 18 

1 1 .  Discharging  into  Rivers  and  Tidal  Waters 20 

1 2.  Sewage  Treatment 26 

CHAPTER  III.    AMOUNT  OF  SEWAGE. 

13.  Sewerage  Conduits 30 

14.  Amount  of  House-sewage 31 

1 5.  Data  of  House-sewage  Flow 37 

16.  Amount  of  Storm-water 44 

17.  Rates  of  Rainfall _    44 

18.  Run-off  Data 47 

19.  Formulas  for  Storm- water  Run-off 52 

20.  Expediency  of  Providing  for  Excessive  Storms 56 

v 


VI  CONTENTS. 


CHAPTER  IV.    FLOW  IN  SEWERS. 

ART.  PAGE 

21.  Fundamental  Theories 60 

22.  Limits  of  Velocity 73 

23.  Size  of  the  Sewer 78 

24.  Shape  of  the  Sewer 81 


CHAPTER  V.    FLUSHING  AND  VENTILATION. 

25.  Necessity  for  Flushing 85 

26.  Methods  of  Flushing 88 

27.  Appliances  for  Flushing 93 

28.  Necessity  for  Ventilation 95 

29.  Methods  of  Ventilation 97 


CHAPTER  VI.    COLLECTING  THE  DATA. 

30.  Data  Required 103 

31.  Surveying  and  Plotting 106 


CHAPTER  VII.    THE  DESIGN. 

32.  General  Principles 1 1 1 

33.  Subdivision  into  Districts 1 16 

34.  Locating  the  Sewer  Lines 117 

35.  Volume  of  House-sewage 1 20 

36.  Volume  of  Storm-sewage 122 

37.  Grade,  Size,  and  Depth  of  Sewers 131 

38.  Inverted  Siphons 1 38 

39.  Sub-drains 139 

40.  House  and  Inlet  Connections 141 

41.  Manholes,  Inlets,  Flush-tanks,  etc 144 

42.  Pumping  of  Sewage 148 

43.  Intercepting-sewers  and  Overflows .  153 

44.  Use  of  Old  Sewers 155 

CHAPTER  VIII.    DETAIL  PLANS. 

45.  The  Sewer-barrel 157 

46.  Pipe  Sewers 166 

47.  Manholes,  Lamp-holes,  Flush-tanks,  etc 171 

48.  Interceptors  and  Overflows 183 

49.  Inverted  Siphons,  Sub-drains,  Foundations 185 


CONTENTS.  Vll 


CHAPTER  IX.    SPECIFICATIONS,  CONTRACT,  ESTIMATE 
OF  COST. 

ART.  PAGE 

50.  Definition  and  Classification  of  Specifications 190 

5 1 .  Specifications  for  Materials 1 92 

52.  "  "    Excavation 198 

53.  "  "    Construction 202 

54.  "  "   Back-filling  and  Cleaning  Up 212 

55.  General  Provisions,  Payments,  etc 216 

56.  Contract 223 

57.  Estimate  of  Cost 226 

58.  Methods  of  Assessment. ...    231 


PART   II.    CONSTRUCTION. 
CHAPTER  X.    PREPARING  FOR  CONSTRUCTION. 

59.  Contract  Work  or  Day  Labor 237 

60.  Obtaining  Bids 239 

61.  Engineering  Work  Preliminary  to  Construction 241 

62.  Other  Preliminaries 242 

CHAPTER  XI.    LAYING  OUT  THE  WORK. 

63.  Lining  Out  Trenches 244 

64.  Giving  Grade 245 

CHAPTER  XII.    OVERSIGHT  AND  MEASUREMENT  OF  WORK. 

65.  Inspection  of  Work ; 252 

66.  Duties  of  the  Engineer , 254 

67.  Measurements 256 

68.  Final  Inspection 260 

CHAPTER  XIII.    PRACTICAL  SEWER  CONSTRUCTION. 

69.  Organizing  the  Force 265 

70.  Trenching  by  Hand 270 

71.  Excavating  Machinery 275 

72.  Sheathing., 279 

73.  Laying  Sewer  Pipe 291 

74.  Building  Masonry  Sewers 297 

75.  Building  Manholes  and  Other  Appurtenances 306 


Vl.ll  CONTENTS. 

ART.  PACK 

76.  Foundations 309 

77.  Pumping  and  Draining 310 

78.  Handling  Wet  and  Quicksand  Trenches 315 

79.  River  Crossings  and  Outlets 328 

80.  Crossing  Railroads  and  Canals * 335 


PART  III.     MAINTENANCE. 
CHAPTER  XIV.    HOUSE  CONNECTIONS  AND  DRAINAGE. 

81.  Necessity  for  Intelligent  Maintenance 340 

82.  Requirements  of  Sanitary  House-drainage 341 

CHAPTER  XV.  SEWER  MAINTENANCE. 

83.  Requirements  of  Proper  Maintenance 347 

84.  Flushing 349 

85.  Cleaning 354 

TABLES. 

1.  Population   and  Per  Capita   Water  Consumption  in   Different 

Cities c 32 

2.  Population,  Number  per   Family  and   per   Dwelling,   Different 

Cities 35 

3.  Gaugings  of  Sewage  Flow,  Providence,  R.  1 38 

4.  "         "       "             "     Toronto,  Canada 39 

5.  "         "                    "     Schenectady,  N.  Y 39 

6.  "          "       "             "      Atlantic  City,  N.  J 39 

7.  "         "       "             "     Weston,  W.  Va.,  Insane  Hospital. .    .  40 

8.  "         "       "            and  Water  Consumption,  Des  Moines,  la.  43 

9.  Maximum  Rates  of  Rainfall  in  Various  Sections 46 

10.  Relative  Cost  and  Capacity  of  Sewers,  Washington,  D.  C... . . .  58 

11.  Velocity  and  Discharge  in  Circular  Sewers,  4  to  36  in.  Diameter  64 

12.  "        "            "          "           "            "  33  in.  to  10  ft.  Diameter  66 

13.  p,  a,  -R,  Velocity  and  Discharge  for  Different  Depths  of  Sew- 

age, Circular  Sewers 69 

14.  p,  a,  7vJ,  Velocity  and  Discharge  for  Different  Depths  of  Sewage 

Egg-shaped  Sewers 70 

15.  Materials  Moved  by  Different  Velocities  of  Water 74 

16.  Calculation  of  Sewer  Sizes  for  Minimum  Grades ,  134 

17.  Prices  and  Weights,  Vitrified  Clay  Sewer-pipe 227 


CONTENTS,  IX 


18.  Prices  of  Drain-tile.. 228 

19.  "       "    Light-weight  Iron  Pipe  . 228 

20.  Amount  of   Cement  for  Laying  Different  Sizes  of  Sewer-pipe  228 

21.  Cost  of  Excavating,  Back-filling,  and  Sheathing  Trenches 229 

22.  Cost  of  Laying  Sewer-pipe 229 

23.  Cost  of  Circular  Brick  Sewers 230 

24.  Cost  of  Manholes 230 


ILLUSTRATIONS. 

PLATE 

I.  Des  Moines  Sewer  Gaugings  and  Water  Consumption 41 

II.  New  Orleans  Run-off  Curve  Diagrams 49 

III.  Plan  of  a  House-sewerage  System 123 

IV.  Rainfall  Diagrams  and  Acreage  Curve 125 

V.  Plan  of  a  Storm  Sewer  System 128 

VI.  Sections  of  Masonry  Sewers 160 

VII.           "        "          "              "     : 162 

VIII.           "        "          "          and  Pipe  Sewers 164 

IX.   Manholes  and  Lamp-holes. 173 

X.   Manholes,  Flush-tanks,  and  Inlets 175 

XI.    Interceptors,  Siphons,  Sub-drains,  etc ,    ..  184 

XII.  Trestle  Excavating-machine  at  Work 277 

FIGURE 

1.  Modified  Birmingham  Pail     5 

2.  Egg-shaped  Sewer 82 

3.  Sounding-rod 109 

4.  Alignment  of  Sewer  Junctions 119 

5.  Method  of  Setting  Grade-plank 246 

6.  "       "         "  "          " 247 

7.  "       "   Holding  Grade-cord 248 

8.  Grade-rod 248 

9.  Inspector's  Templet,  Egg-shaped  Sewer 262 

10.  Invert-former. 263 

1 1 .  Excavation-platform 271 

1 2.  Cross-staging  in  Trench 272 

13.  Skeleton  Sheathing 281 

14.  Sheathing  under  Braces 283 

1 5.  Driving-cap  and  Maul , 285 

16.  Horizontal  Sheathing 285 

17.  Sliding  Rod  for  Measuring  Braces 287 

18.  Sheathing  Puller 289 

19.  Pipe-laying  Hook 292 

20.  Appliance  for  "Entering"  Heavy  Pipe 292 


X  CONTENTS. 

FIGURE  PAGE 

21.  Pipe-cleaning  Disk 295 

22.  Templet  for  Brick  Sewers 298 

23.  Hod  for  Lowering  Brick 300 

24.  Mason's  Platform  for  Brick  Sewers 301 

25.  Centre  for  Brick  Sewers 302 

26.  Form  for  Concrete  Arch 305 

27.  Sewer-pipe  Laid  in  Concrete 319 

28.  Sheathing  a  Badly  Caved  Trench .' 32 1 

29.  Appliance  for  Cleaning  Sub-drains 326 

30.  Sewer  Crossing  Creek  above  Water 329 

31.  Coffer-dam  Puddle  Walls 333 

32.  Sheathing  on  Steep  Slopes 337 

33.  Flange  for  Pipe  in  Embankment 338 

34.  Appliance  for  Cleaning  Siphon-sump 355 

35.  Disk  for  Cleaning  Sewers 357 

36.  Method  of  Using  Cleaning-disk 358 


SEWERAGE. 


CHAPTER  I. 
THE    SYSTEM. 

ART.  1.     REQUIREMENTS  OF  A  SYSTEM. 

A  SYSTEM  for  the  removal  of  sewage  is  demanded  by  a 
populous  community  on  two  grounds:  the  higher  one  of  the 
public  health,  and  the  more  popular  one  of  convenience;  and 
in  designing  a  system  each  of  these  purposes  must  be  kept 
constantly  in  mind,  the  first  being  ever  given  predominance 
over  the  second  if  they  conflict  in  any  way.  The  proper 
meeting  of  these  demands  determines  the  principles  of 
designing. 

There  are  two  imperative  essentials  to  sanitary  sewerage: 

I.  That  the  sewage,  and  all  the  sewage,  be  removed  with- 
out any  delay  to  a  point  where  it  may  be  properly  disposed 
of. 

II.  That  it  be  so  disposed  of  as  to  lose  permanently  its 
power  for  evil. 

Convenience  requires  that  the  sewage  be  collected  and 
disposed  of  with  the  least  trouble  to  the  householder  and  in 
the  least  obtrusive  and  offensive  way. 

In  taking  up  the  study  of  sewerage  for  any  particular 
place  or  community  the  first  question  arising  is  the  general 


2  SEWERAGE. 

system  to  be  adopted.  In  many  cases  financial  limitations 
will  be  forced  upon  the  engineer  as  an  unfortunate  but  im- 
perative argument  in  the  choice  not  only  of  the  details  of  the 
system  but  even  of  the  system  itself.  He  must  perforce 
recognize  these  limitations  in  addition  to  the  requirements  of 
sanitation  and  convenience,  but  should  not  carelessly  assume 
that  since  there  is  but  little  money  to  spend  upon  the  work 
the  care  given  to  the  design  will  need  to  be  only  proportion- 
ately great.  He  should  realize  that  the  highest  talent  is 
needed  to  obtain  the  best  results  with  limited  resources. 

The  solution  of  the  difficulty  when  a  complete  water- 
carriage  system  is  rendered  out  of  the  question  by  reason  of 
its  cost  may  lie  in  the  construction  of  only  the  most  neces- 
sary portion  of  the  system  or  in  the  adoption  of  one  of  the 
dry-sewage  systems. 

ART.  2.     DRY  SEWAGE  METHODS. 

The  methods  in  common  use  for  removing  excrement  and 
liquid  wastes  may  be  conveniently  divided  into  three  general 
classes:  (i)  Dry  Sewage,  (2)  Pneumatic,  and  (3)  Water-car- 
riage systems. 

The  most  primitive  method  of  application  of  excrements 
to  the  soil — if  it  can  be  called  a  method — would  be  embraced 
under  the  first  head.  The  old-fashioned  privy  was  a  step 
forward,  and  in  a  large  part  of  this  country  is  as  yet  the  only 
one  which  has  been  taken,  privacy  being  the  main  argument 
for  its  adoption.  But,  while  contributing  somewhat  to  this 
and  to  comfort,  it  cannot  be  considered  as  a  sanitary  appli- 
ance. "  Constructed  for  the  avowed  purpose  of  retaining  the 
solid  matters  as  long  as  possible  upon  the  premises,  they 
become  centres  of  pollution  and  infection.  The  liquid  por- 
tions, escaping,  pollute  the  soil  and  neighboring  wells;  the 
noxious  exhalations  arising  from  their  putrefying  contents 


THE    SYSTEM. 

contaminate  the  air."  (Samuel  M.  Gray's  Report  on  Pro- 
posed Sewerage  System  for  Providence,  R.  I.) 

Regular  movement  of  the  bowels  is  essential  to  health  and 
to  bodily  and  mental  vigor.  Yet  a  rainy  day,  a  deep  snow, 
or  publicity  of  location  has  kept  many  a  person  from  the  daily 
attention  to  nature's  demands  when  this  requires  a  visit  to 
the  outdoor  privy. 

This  last  objection  is  met  by  the  indoor  closet  connected 
with  a  cesspool;  but  there  is  probably  no  subject  upon  which 
sanitarians  are  more  thoroughly  agreed  than  upon  the  inher- 
ent vileness  and  danger  of  the  cesspool  as  ordinarily  con- 
structed. Fresh  sewage  if  not  taken  into  the  stomach  is 
neither  injurious  to  health  nor  very  offensive  to  the  smell ; 
but  from  putrescent  excreta  and  kitchen  slops  come  those 
noisome  gases  which,  if  not  themselves  bearers  of  malefic 
germs,  at  least  lower  the  vitality  and  render  the  body  more 
vulnerable  to  disease.  Retained  for  weeks  and  months  in  a 
liquid  or  semi-liquid  state  in  a  cesspool,  sewage  is  then  under 
the  conditions  best  adapted  to  putrefaction  in  its  foulest  form. 
And  in  very  few,  if  any,  cases  is  the  plumbing  of  the  house 
adapted  to  exclude  from  the  air  of  the  dwelling  the  gases 
emitted;  indeed  it  is  doubtful  if  this  can  be  accomplished 
with  certainty  when,  as  is  too  often  the  case,  the  cesspool  is 
tightly  covered  or  sealed  with  snow  or  ice.  Moreover,  prac- 
tically no  cesspools  are  water-tight,  though  many  are  thought 
to  be  so.  A  cesspool  S£  feet  in  diameter  and  10  feet  deep 
to  which  a  family  of  five  contribute  a  daily  average  of  25 
gallons  of  sewage  (a  low  estimate)  would,  if  tight,  require  to 
be  cleaned  twice  each  year.  Very  few,  it  is  believed,  are 
cleaned  this  often;  many  are  never  cleaned,  but  the  contained 
liquid  leaches  out  into  and  through  the  adjacent  soil,  which 
soon  loses  its  power  to  purify  it. 

This  vilest  of  liquids  is  dangerous  in  two  ways :  it  may 
reach  and  taint  wells  for  hundreds  of  feet  around,  and  it  may 


4  SEWERAGE. 

pollute  the  air  existing  in  the  soil  under  cellars,  which  air  will 
exhale  and  permeate  the  houses  above.  In  excavating  for 
sewers  in  gravelly  soil  in  a  city  street  the  author  has  found 
the  gravel  colored  black  by  the  liquid  from  a  cesspool  located 
75  feet  distant  in  the  rear  of  the  house  opposite;  which 
liquid  must  consequently  have  passed  under  or  around  the 
cellar  of  this  house. 

It  seems  advisable  to  speak  thus  at  length  on  this  subject 
for  the  reason  that  many  intelligent  persons  look  with  favor 
on  the  cesspool  as  a  sanitary  contrivance,  whereas  in  most 
cases  it  is  one  of  the  greatest  abominations  permitted  in  any 
civilized  community. 

ART.  3.     DRY  SEWAGE  SYSTEMS. 

« 

The  methods  already  referred  to  can  hardly  be  called 
systems,  but  are  rather  makeshifts.  The  simplest  systems 
which  can  be  at  all  commended  are  the  Pail  system  and  the 
Earth-closet.  These  are  used  but  little  in  this  country,  but 
would  be  for  many  small  villages  a  vast  improvement  over 
the  privy  or  cesspool. 

The  Pail  system  consists  essentially  of  the  placing  under 
the  privy-seats  of  pails,  which  are  to  be  removed,  emptied  in 
some  spot  where  a  nuisance  will  not  thereby  be  created, 
cleaned,  and  returned.  Duplicate  pails  must  be  provided  to 
be  used  in  place  of  these  during  their  absence. 

This  method  is  in  use  at  Marseilles,  Havre,  and  other 
French  cities;  at  Rochdale,  Birmingham,  Manchester,  and 
other  places  in  England;  but  only  in  certain  districts  of  these 
cities,  which  are  introducing  water  carriage  and  are  yearly 
increasing  the  territory  thus  sewered.  It  has  been  used  by 
a  few  communities  in  this  country  also,  among  them  Vine- 
land,  N.  J. ;  but  this  place  also  will  probably  replace  it  with 
a  water-carriage  system. 


THE   SYSTEM. 


A  modification  of  and  improvement  upon  the  Pail  system 
is  the  Earth-closet  system,  in  which  pulverized  dry  earth, 
charcoal,  or  ashes  are  used  as  a  deodorizer  and  are  applied  to 
the  excreta  while  fresh,  the  mixture  being  subsequently 
removed,  preferably  as  in  the  Pail  system.  Brick-clay  and 
loam  rank  high  as  deodorizers  when  applied  in  a  perfectly 
dry  and  powdered  state.  Ashes  are  not  so  effective.  In 
Bremen  powdered  turf  is  used.  There  is  not  evident  a  suffi- 
cient superiority  in  charcoal  to  compensate  for  its  cost  and 
other  disadvantages. 

The  deodorizing-powder  should  be  applied  each  time  the 
closet  is  used.  An  excellent  arrangement  is  that  of  a  large 
box  or  barrel  resting  upon  an  extension  of  the  seat  and  with 
an  aperture  and  slide  so  contrived  that  any  desired  amount 
of  the  powder  may  be  deposited  upon  the  excrement  by  a 


i 


i 


18 


FIG.  i. — MODIFIED  BIRMINGHAM  PAIL. 

slight  motion  of  a  convenient  handle.  The  simplest  method 
of  applying  the  deodorizer  is  by  a  small  scoop  or  shovel,  the 
earth  being  kept  in  a  box  placed  in  a  convenient  position  in 
the  closet. 

For  either  the  Pail  or  Earth-closet  system  the  receptacle 
should  be  round,  as  this  form  is  more  easily  cleaned  than  a 
square  one;  and  preferably  of  metal,  as  a  wooden  pail  soon 


6  SEWERAGE. 

becomes  saturated  with  foul  liquors.  A  good  form  is  that  of 
the  modified  Birmingham  pail.  The  pails  should  be  thor- 
oughly cleaned  after  each  emptying.  If  the  earth  closet  is 
used  a  thin  layer  of  earth  should  be  spread  over  the  bottom 
of  the  pail  when  it  is  replaced  under  the  seat. 

The  mixture  of  earth  and  excreta  may  be  dried  and  used 
again;  but  there  is  a  possible  danger  in  this,  since  bacteria 
are  not  often  destroyed  by  moderate  heat;  it  will  probably 
be  found  more  convenient  also  to  deposit  it  immediately  upon 
the  garden  or  field  as  a  fertilizer.  If  the  Pail  or  Dry-earth 
system  is  adopted  for  a  village  or  city  an  arrangement  may 
be  made  by  contract  for  removing  the  buckets  or  tubs  at 
intervals  of  not  more  than  a  week,  the  material  to  be  disposed 
of  by  the  contractor.  Such  disposition  of  it  should  be  made 
— either  by  placing  it  directly  upon  the  fields;  or  by  drying 
and  pulverizing  it,  in  which  form  (poudrette)  it  is  more  con- 
venient for  use  as  a  fertilizer;  or  by  burning  it  (see  Chapter 
II) — as  will  avoid  the  creating  of  a  nuisance  (see  Art.  10). 

There  are  several  methods,  some  patented,  for  disposing 
of  dry  sewage  and  garbage  on  the  premises  by  means  of  heat, 
by  either  drying  or  cremating.  The  heat  for  these  is 
obtained  either  from  a  furnace  constantly  burning,  in  which 
case  its  use  in  summer  is  exceedingly  inconvenient  and  is 
usually  dispensed  with;  or  by  occasional  fires  lighted  at  long 
intervals,  during  which  the  waste  matter  undergoes  dangerous 
putrefaction.  On  account  of  these  and  other  equally  serious 
objections  these  methods  are  not  to  be  commended,  particu- 
larly since  the  cost,  were  every  house  to  adopt  them,  would 
in  most  locations  suffice  to  construct  an  excellent  water- 
carriage  system. 

These  dry-sewage  systems,  though  improvements  on  the 
privy  and  cesspool,  are  imperfect  from  a  sanitary  point  of 
view  in  that  they  require  the  excreta  to  be  stored  about  the 
premises  for  a  certain  period,  and  because  they  fail  to  pro- 


THE   SYSTEM.  7 

vide  for  the  removal  of  slops  and  sink-water  and  dispose  of 
urine  to  a  limited  extent  only.  Neither  do  they  provide 
for  the  drainage  of  the  soil  nor  for  the  removal  of  surface- 
water.  Convenience  also  is  not  fully  served  by  their  use. 

ART.  4.     PNEUMATIC  SYSTEMS. 

In  the  Pneumatic  systems  the  faeces  only  are  removed, 
the  house  drainage,  surface-  and  subsoil-water  requiring  a 
separate  system  of  sewers  or  utilizing  the  gutters.  The  most 
widely  known  of  these  are  the  Liernur  and  the  Berlier — the 
first  used  principally  in  Holland,  the  second  in  Paris.  These 
two  are  practicable  under  certain  conditions  only  and  will  not 
be  described  at  length.  Their  object  is  to  remove  the  sew- 
age at  frequent  intervals  through  pipes,  by  means  of  com- 
pressed air  or  a  vacuum,  to  a  central  station,  there  to  be 
disposed  of  in  some  way,  usually  by  being  manufactured  into 
a  fertilizer.  The  great  cost  of  these  is  prohibitive  to  their 
introduction  into  small  cities  and  towns,  and  on  account  of 
their  limited  applicability,  as  well  as  for  practical  and  sanitary 
reasons,  their  adoption  in  future  designs  is  improbable. 

The  Shone  system,  which  is  used  to  some  extent  in 
England  and  her  colonies  and  in  this  country,  although 
classed  among  the  Pneumatic  systems,  is  really  not  in  itself  a 
system,  but  an  application  to  the  water-carriage  system  of  a 
method  of  pumping  sewage  by  the  direct  action  of  com- 
pressed air.  It  will  therefore  be  considered  under  the  head 
of  the  Water-carriage  System. 

ART.  5.     WATER-CARRIAGE  SYSTEM. 

The  Water-carriage  system  has  now  been  so  almost  uni- 
versally adopted  where  any  improvement  upon  the  primitive 
privy  has  been  attempted  that  the  term  "  Sewerage  System  " 


8  SEWERAGE. 

is  ordinarily  used  without  further  qualification  to  refer  to  it. 
When  properly  constructed  and  managed  it  is  certainly 
deserving  of  its  popularity,  being  the  best  and  cheapest 
method  yet  contrived  for  the  removal  of  sewage. 

As  its  name  implies,  its  distinctive  characteristic  is  the 
removal  through  conduits,  by  gravitation,  of  sewage  which 
has  been  greatly  diluted  with  water.  It  meets  the  first 
principal  requirement  of  a  sanitary  system  (Art.  i) — it 
removes  all  house-wastes  and  removes  them  immediately.  It 
also  serves  the  secondary  but  by  no  means  unimportant  pur- 
pose of  removing  the  surface-water  and  draining  the  ground. 
Its  convenience  also  is  excelled  by  no  other  system.  More- 
over, where  the  territory  is  quite  thickly  populated — as  in 
the  average  town — it  is  in  the  end  cheaper  than  any  other 
system.  The  two  most  weighty  arguments  against  it  are  the 
large  amount  of  water  needed  for  its  efficient  working,  and 
the  pollution  of  streams  and  waste  of  the  valuable  manurial 
properties  in  the  sewage  when  this  is  emptied  into  river  or 
sea,  as  is  frequently  done.  Victor  Hugo  in  his  "  Les 
Miserables  "  devotes  a  long  chapter  to  the  "Crime  of  the 
Century"  involved  in  this  waste.  But  whether  this  matter 
is  ultimately  wasted  or  its  use  by  man  only  deferred  it  is  not 
necessary  to  discuss.  The  all-convincing  argument  with  any 
but  the  sentimentalist  is  that,  while  there  may  be  manurial 
value  in  sewage,  no  commercially  profitable  method  of  utili- 
zing it  has  yet  been  found.  The  best  disposition  to  be  made 
of  it  is  therefore  that  which  is  least  harmful,  unpleasant,  and 
expensive,  and  in  most  cases  water  carriage  enables  us  to 
provide  such  disposition. 

The  argument  that  its  proper  working  involves  the  use  of 
large  quantities  of  water  is  undoubtedly  true.  But  where 
water-works  already  exist  this  objection  has  little  force — less 
in  this  country  than  abroad,  where  20  to  40  gallons  per  capita 
is  considered  a  liberal  allowance  for  water-consumption; 


THE   SYSTEM.  9 

while  in  this  country  our  small  cities  must  provide  two  or 
three  and  the  large  ones  five  or  six  times  this  amount,  which, 
with  in  many  cases  a  small  percentage  additional  for  flushing, 
is  usually  sufficient  and  no  difficulty  is  found  in  providing  it. 
Some  expense,  however,  is  frequently  incurred  for  flushing- 
water  and  to  this  extent  is  there  force  to  the  objection. 

Places  which  are  without  a  general  water-supply  or  the 
general  use  of  individual  power-supplies  are  barred  from  the 
adoption  of  the  Water-carriage  system.  For  such  the  best 
plan  is  to  adopt  the  Earth-closet  system  until  such  time  as 
water  has  been  introduced  into  most  of  the  dwellings,  when 
a  Water-carriage  system  may  be  initiated,  the  Earth-closet 
pails  being  continually  relegated,  as  the  conduit  system  is 
extended,  to  the  outskirts  of  the  town,  where  the  growth  will 
probably  keep  a  year  or  two  ahead  of  the  water-supply  and 
sewer-construction. 

Other  objections  are  sometimes  raised  to  the  Water- 
carriage  system  which  are  either  equally  applicable  to  all 
systems  or  which  are  the  result  c-f  prejudice.  The  possibility 
of  the  introduction  into  dwellings,  through  the  house-connec- 
tions, of  sewer-air  (which  is  not  a  "  gas")  is  one  of  these, 
and  is  certainly  a  real  one.  But  the  resulting  danger  is  not 
so  great  as  that  connected  with  similar  evils  of  other  systems, 
and  it  is  preventable  by  careful  designing  and  construction  of 
the  sewers  and  house-plumbing. 

ART.  6.     COMBINED  AND  SEPARATE  SYSTEMS. 

It  is  generally  conceded  by  sanitarians  that  where  the 
conditions  render  it  possible  the  Water-carriage  system  should 
be  adopted.  This  system,  however,  has  been  subdivided 
into  the  Combined  and  the  Separate  systems.  The  terms 
"  Combined"  and  "  Separate"  refer  to  the  two  classes  of 
waters  which  it  is  desirable  to  remove — rain-water  and  house- 


IO  SEWERAGE. 

sewage.  In  the  former  system  these  are  carried  in  a  common 
conduit;  in  the  latter  the  house-sewage  is  removed  through 
small  sewers,  the  storm-waters  through  other  large  ones  or  in 
the  gutters,  or  partly  in  one  and  partly  in  the  other. 

The  comparative  merits  of  these  is  a  theme  much  dis- 
cussed and  upon  which  unanimity  of  opinion  has  not  yet  been 
entirely  reached.  It  will  most  probably  be  reached  by 
mutual  concession,  for  there  are  undoubtedly  substantial 
arguments  in  favor  of  each.  In  some  cases  the  one,  in  some 
the  other,  is  most  applicable.  In  many,  if  not  a  majority  of, 
instances  a  judicious  combination  of  the  two  will  work  to 
better  advantage  than  either  alone. 

There  is  neither  space  nor  necessity  to  quote  in  this  work 
all  the  arguments  advanced  for  and  against  each  of  the 
systems,  or  even  to  attempt  to  specify  them  all  in  detail, 
since  the  systems  will  be  treated  as  cooperative  rather  than 
as  rivals;  for  such  is  the  relative  position  now  assigned  them 
by  the  best  authorities.  Their  respective  advantages  under 
varying  conditions  will  be  treated  of  in  Chapters  III  and  VII. 
It  may  be  well,  however,  to  give  in  this  connection  a  short 
statement  of  the  points  at  issue  between  the  two  systems. 

Either  system  must,  if  providing  for  storm-water,  include 
sewers  of  large  size — 2,  3,  even  15  or  20  feet  in  diameter. 
Yet  during  nine  tenths  of  the  time  the  amount  of  sewage 
flowing  is  no  more  than  could  be  carried  by  pipes  of  from  4 
inches  to  2  feet  in  diameter. 


(i)  In  the  Separate  system 
pipes  of  that  size  are  used  for 
the  daily  sewage,  and  thus 
greater  velocity  secured  with 
a  given  amount  of  sewage  and 
a  given  grade;  consequently 
cleaner  sewers. 


(2)  But  even  these  will  at 
times  stop  up,  and  then  there 
may  be  some  difficulty  in  re- 
moving obstructions  from  the 
pipes.  Obstructions  in  the 
large  sewers  on  the  other  hand 
can  be  readily  reached  and 
removed. 


THE   SYSTEM. 


II 


(2)  But  in  the  Separate 
system  the  storm-sewers  may 
frequently  be  placed  only  3 
to  5  feet  below  the  surface, 
while  in  the  Combined  they 
must  be  low  enough  to  receive 
the  house-sewage  —  usually 
from  8  to  12  feet  belowthe  sur- 
face. The  resulting  increase 
in  cost  would  often  more 
than  cover  that  of  an  addi- 
tional system  of  small  house- 
sewers.  Moreover,  towns  too 
poor  to  put  in  large  Combined 
sewers  can  for  one  third  to 
one  fifth  of  their  cost  remove 
their  daily  sewage  alone  by 
means  of  small  pipes. 

(2)  But  flushing  would  im- 
prove Combined  Sewers  also, 
and  would  probably  be  em- 
ployed if  the  amount  of  water 
necessary  to  keep  them  clean 
were  not,  through  its  vastness, 
prohibitive,  unless  it  can  be  in- 
troduced from  a  river  or  other 
large  body  of  water,  a  plan 
which  is  sometimes  adopted. 

(2)  If  each  is  running  full; 
but  with  a  given  amount  of 
sewage  the  larger  sewer  must 
have  the  steeper  grade  if  the 
same  velocity  is  to  be  ob- 
tained. 


(i)  In  the  Separate  sys- 
tem the  storm-sewers  must  be 
as  large  as  those  of  the  Com- 
bined and  an  additional  small 
sewer  be  provided  at  a  cost 
which  increases  by  its  full 
amount  the  cost  of  the  Sepa- 
rate over  that  of  the  Combined 
system. 


(i)  The  Separate  system 
usually  requires  large  quanti- 
ties of  water  for  its  perfect 
operation. 


(i)  For  small  sewers  steep- 
er grades  are  necessary  than 
for  large  ones. 


12 


SE  WERA  GE. 


(2)  But  this  fault  (when  it 
is  a  fault)  is  one  of  the  de- 
signer, and  not  of  the  system. 


(1)  There  is  a  tendency  in 
using  the  Separate  system  to 
allow  storm-water  to  run  for 
long  distances  upon  the  street- 
surface. 

(2)  But    foul   air  is  more 
diluted  in  large  ones. 

(2)  But  on  the  other  hand 
street-washings  are  often  as 
foul,  though  not  usually  as 
dangerous,  as  house-sewage, 
and  should  be  purified. 


(i)  Ventilation  is  more 
rapid  in  small  sewers. 

(i)  A  very  important  ar- 
gument in  favor  of  the  Sepa- 
rate system,  and  one  which 
has  the  backing  of  the  law  in 
many  States,  is  the  practical 
necessity  for  its  use  where 
treatment  of  the  house-sew- 
age is  either  immediately 
necessary  or  may  in  future  be- 
come so. 

Many  other  arguments  have  been  advanced  on  both  sides, 
but  the  most  weighty  in  favor  of  the  Combined  system  are: 
its  economy  in  first  cost  over  two  Separate  systems,  and  the 
ease  with  which  obstructions  can  be  removed  and  a  general 
examination  of  its  contents  made;  in  favor  of  the  Separate 
system :  its  being  self-cleansing,  its  adaptability,  as  a  house- 
sewage  system  only,  to  small  and  poor  towns,  and  its  necessity 
to  an  economical  sanitary  treatment  of  the  house-sewage. 


ART.  T.     SUMMARY. 

The  proper  conclusion  in  reference  to  the  system  to  be 
adopted  would  seem  to  be — the  water-carriage,  where  its 
expense  is  not  prohibitive  and  the  dwellings  are  abundantly 
supplied  with  water.  In  a  few  exceptional  cases  a  Pneumatic 
system  might  be  preferable.  But  better  than  the  cesspool  or 
privy,  if  the  cost  or  the  water-supply  is  peremptorily  limited, 


THE   SYSTEM.  1 3 

would  be  a  dry-sewage  system — preferably  the  dry-earth. 
The  last  is  described  to  a  sufficient  length  in  this  chapter, 
as  the  proper  conduct  of  it  requires  little  else  than  cleanliness 
and  faithful  attention.  The  disposal  of  sewage  thus  collected 
will,  however,  be  referred  to  in  Chapter  II. 

The  water-carriage  system  is  more  complicated  in  design, 
in  construction,  and  in  operation;  and  to  the  consideration  of 
this  system  the  remainder  of  this  work  will  be  devoted. 


CHAPTER   II. 
SEWAGE  DISPOSAL. 

IT  is  not  intended  to  give  a  complete  treatise  on  the  sub- 
ject of  sewage  disposal.  To  do  so  would  double  the  size  of 
this  book;  moreover,  the  subject  has  been  most  ably  treated 
by  others  (see  "  Sewage  Disposal  in  the  United  States,"  by 
Rafter  and  Baker;  "  Sewage  Treatment,  Utilization,  and 
Purification/'  by  J.  W.  Slater;  "Sewage  Disposal,"  by 
Wynkoop  Kiersted;  "  Sewage  Disposal  Works,"  by  W.  Santo 
Crimp;  also  Reports  of  the  Massachusetts  State  Board  of 
Health).  It  is  thought  advisable,  however,  to  give  a  short 
statement  of  the  present  knowledge  and  practice  on  the 
subject,  since  the  design  of  the  sewerage  system  will  de- 
pend to  a  certain  extent  on  the  method  of  disposal  adopted. 

ART.  8.     "DISPOSAL  '  AND  "SEWAGE"  DEFINED. 

» 

The  word  disposal  is  often  used  where  treatment  would 
be  more  properly  employed.  As  a  matter  of  fact  all  sewage, 
dry  or  water-carried,  must  be  disposed  of  in  some  way  after 
having  been  collected  by  a  sewerage  system.  But  if  this  dis- 
posal consists  of  anything  other  than  throwing  away  the 
sewage  this  may  be  properly  called  a  treatment  thereof. 
These  words  will  be  thus  used  in  this  work — disposal  as  a 
general  term,  treatment  as  a  more  specific  one. 

14 


SEWAGE 

For  a  proper  consideration  of  the  various  methods  of  dis- 
posal it  will  be  necessary  to  understand  the  results  aimed  at 
and  the  principles  involved.  And  first  we  must  understand 
what  is  implied  by  the  word  sewage.  In  the  dry  sewage  and 
pneumatic  systems  it  means  human  excreta  and  nothing  else. 
In  the  water-carriage  system,  however,  sewage  may  be  found 
to  contain  almost  every  description  of  waste  matter:  faeces, 
house-4 *  slops,"  manufacturing  waste- waters  and  acids,  drain- 
age of  stables,  piggeries,  and  slaughter-houses,  waste  paper  and 
rags,  and  frequently  "  swill,"  and  numberless  matters  which 
should  never  reach  the  sewer.  This  is  ordinarily  called  house- 
sewage.  Into  combined  and  storm  sewers,  besides  rain- 
water, not  only  horse-droppings  and  vegetable  refuse  but 
sand,  clay,  gravel,  and  other  heavy  matters  find  admission 
through  the  street-inlets.  These  go  to  make  what  is  called 
storm-sewage.  The  common  impression  is  that  of  these  the 
human  excrements  alone  are  dangerous;  and  this  is  to  a  large 
extent  true  so  far  as  concerns  dissemination  of  the  germs  of 
disease.  But  it  is  known  that,  aside  from  this,  kitchen-wastes 
are  fully  as  dangerous,  since  they  contain  practically  the 
same  putrescible  matter,  and  in  a  state  less  easily  rendered 
innocuous  by  either  natural  or  artificial  means.  Where  storm- 
water  is  admitted  to  the  sewers  the  large  quantities  of  horse- 
droppings  which  are  washed  in  during  the  first  few  minutes 
of  each  rainstorm  render  the  water  nearly  as  offensive,  if  not 
so  dangerous,  as  do  human  excreta. 

Owing  to  diversity  of  manufacturing  industries,  to  differ- 
ences in  the  characters  of  the  water  used  by  different  towns, 
and  to  other  local  peculiarities  the  sewage  of  each  town  varies 
from  that  of  almost  every  other.  Therefore  the  question  of 
the  proper  disposal  of  this  compound  is  seen  to  be  a  problem 
of  no  easy  solution.  The  difficulty  of  treatment  is  increased 
by  the  exceeding  dilution  of  the  sewage,  since  the  sewage  of 
an  average  American  town  will  contain  but  about  I  part  in 


1 6  SEWERAGE. 

1000  of  organic  matter,  I   part  of  mineral  matter,  and  998 
parts  of  water. 

In  this  chapter  house-sewage  only  is  considered,  as  there 
are  very  few  cases  where  storm-sewage  is  purified.  It  is 
desirable,  however,  to  connect  with  the  house  sewers  cab- 
stands, market-places,  and  other  parts  of  streets  liable  to 
collect  considerable  filth,  small  inlets  being  used,  so  that  only 
a  small  amount  of  water  from  any  storm  can  enter  them,  or 
else  special  traps,  ordinarily  closed,  but  through  which  the 
filth  can  be  washed  by  hose. 

ART.  9.     AIMS  OF  DISPOSAL. 

The  first  aim  is  the  getting  rid  of  the  sewage ;  the  dispos- 
ing of  it  in  such  a  way  and  such  a  place  that  it  will  not  create 
a  nuisance.  Communities,  being  even  more  selfish  than  indi- 
viduals, seldom  regard  the  well-being  of  other  communities, 
but  are  satisfied  if  no  nuisance  is  created  within  their  own 
limits.  It  is  here  that  the  State,  by  its  laws  and  through  its 
Board  of  Health,  should  interfere  for  the  protection  of  each 
community  against  all  others.  In  England  this  protection  is 
afforded  by  national  laws  and  a  national  board.  In  this 
country  many  States  afford  a  certain  amount  of  such  protec- 
tion, varying  from  that  given  by  the  excellent  laws  of  Massa- 
chusetts down  to  the  almost  total  lack  of  any  such  protection 
which  exists  in  many  of  even  the  older  States.  It  is  a  duty 
which  the  engineer  owes  to  humanity  to  educate  the  people 
to  the  importance  of  this  matter;  though  he  will  often  be 
compelled  to  yield,  in  part  at  least,  to  the  selfish  demands  of 
those  for  whom  he  acts,  that  they  be  put  to  no  expense  for 
protection  of  other  communities  not  required  by  State  or 
national  laws. 

Where  this  protection  is  afforded  through  adequate  laws 
properly  enforced  the  disposal  of  the  sewage  must  be  such 


SEWAGE   DISPOSAL.  1 7 

that  it  will  "  lose  permanently  its  power  for  evil."  How 
this  can  best  and  most  economically  be  done  is  the  question 
to  be  solved. 

Many  attempts  have  been  made  at  a  solution  of  this  ques- 
tion of  disposal  which  shall  not  only  meet  the  sanitary 
requirements,  but  which  shall  also  be  financially  remunerative. 
Some  reports  of  success  have  been  heard  of,  but  when  investi- 
gated the  details  are  found  to  be  disappointing.  An  English 
company  which  used  a  method  of  Chemical  Precipitation  was 
reported  as  paying  dividends,  but  inquiry  showed  that  these 
were  but  a  part  of  the  sum  paid  to  the  company  by  the  dis- 
trict for  disposing  of  its  sewage,  and  the  taxpayers  were  but 
little  benefited  in  pocket  by  the  method  employed.  Investi- 
gations of  other  cases  have  resulted  somewhat  similarly.  The.- 
author  knows  of  no  case  where  the  disposal  of  sewage  is; 
accomplished  at  a  profit  to  the  city  or  town.  In  the  case  of 
water-carried  sewage  this  is  not  to  be  wondered  at,  since  the 
value  of  the  manure  contained  in  one  ton  of  Boston's  sewage,, 
for  instance,  is  estimated  to  be  but  one  cent. 

An  exception  must  be  made,  however,  in  the  case  of  the 
Liernur  system.  It  is  reported  of  the  manufacture  of  pou- 
drette  from  a  portion  of  St.  Petersburg's  sewage  (collected 
by  the  Liernur  system)  that  "it  is  a  groundless  assertion 
that  the  manufacture  of  poudrette  does  not  cover  the  costs.'" 
It  is  possible  that  the  force  of  this  statement  should  be  modi- 
fied by  accenting  the  word  "  manufacture."  But  the  official 
reports  of  the  city  of  Amsterdam  (where  the  Liernur  system 
is  used)  state  that  "  the  value  of  the  dust-manure  made  from 
the  sewage  covers  the  whole  working  expense  of  the  system 
and  leaves  a  considerable  margin  besides."  (Report  of  Charles 
Jonas,  United  States  consul-general  in  1894.)  This  is  un- 
doubtedly accounted  for  by  the  fact  that  faeces  only  are  col- 
lected unmixed  with  water  or  unmanurial  matter.  As  stated 
before,  this  system  does  not  fully  meet  the  sanitary  require- 


1 8  SEWEKAGE. 

ments  and  is  not  adapted  to  this  country,  accustomed  as  we 
are  to  the  abundant  use  of  water  and  to  modern  conveniences. 

The  sewage  of  several  of  our  Western  cities  situated  in  the 
*'  desert  "  region  is  disposed  of  for  irrigation  at  a  considerable 
profit.  Los  Angeles,  Cal.,  received  in  1895  a  net  revenue 
therefrom,  above  all  salaries  and  repairs,  of  $1140,  and  in 
1896  of  $943.30.  This,  however,  was  due  to  the  value  of  the 
water  rather  than  of  the  sewage,  and  such  an  income  would 
not  be  received  were  not  water  of  any  kind  of  considerable 
value.  At  Altoona,  Pa.,  where  the  sewage  is  turned  upon  a 
farm  of  56.8  acres  area,  the  rental  obtained  in  1898  for  the 
farm,  including  the  sewage,  was  only  $100.  Few,  if  any, 
farms  in  a  district  where  irrigation  is  not  necessary,  and  on 
which  the  sewage  must  be  turned  in  rainy  as  well  as  in  dry 
weather,  will  bring  any  considerable  rental. 

It  is  possible  that  some  method  may  be  found  which  shall 
accomplish  both  sanitary  and  financial  success  in  the  treat- 
ment of  sewage.  But  the  existence  of  such  an  one  has  not 
yet  been  demonstrated.  This  being  the  case,  the  endeavor 
should  be  to  find  for  each  place  that  method  of  disposal 
which,  under  the  existing  conditions  of  location,  character  of 
sewage,  etc.,  will  best  meet  the  requirements  both  of  the 
State  laws  and  of  the  laws  of  sanitary  science,  and  which  will 
be  least  expensive,  both  first  cost  and  maintenance  being  con- 
sidered. 

ART.  10.     PRINCIPLES  INVOLVED. 

For  an  exposition  of  the  principles  involved  we  must  call 
upon  chemistry,  biology,  bacteriology,  medicine,  and  kindred 
sciences.  Their  teachings,  stated  generally,  are: 

That  matter  in  a  state  of  putrescence  is  harmful  to  human 
life  if  taken  into  the  system. 

That  volatile  emanations  from  such  matter  when  breathed 


SEWAGE  DISPOSAL.  19 

into  the  lungs  lower  the  tone  of  the  constitution  and  render 
it  more  susceptible  to,  if  they  do  not  indeed  directly  occasion, 
disease. 

That  many  diseases  may  be  contracted  by  taking  into  the 
stomach  certain  germs  which  are  found  to  be  excreted  by 
those  already  sick  of  such  a  disease,  and  these  germs  will 
exist  for  days  in  sewage  having  any  amount  of  dilution. 

That  ordinarily  sewage  does  not  putresce  until  from 
twenty-four  to  sixty  hours  after  its  discharge,  or  even  longer 
under  certain  circumstances,  such  as  absence  of  moisture. 

That  the  only  true  destruction  of  the  dangerous  character- 
istics of  sewage  is  that  effected  by  oxidation  and  by  removal 
of  the  disease-germs. 

That  oxidation  does  not  destroy  but  merely  transforms 
the  putrescible  organic  matter  into  harmless  mineral  com- 
pounds. 

The  legal  principles  involved  vary  in  different  localities 
and  with  different  interpreters  of  the  law,  frequently  depend- 
ing upon  the  ruling  as  to  what  creates  a  nuisance.  "  I  should 
include  under  this  head  any  matter,  whether  solid,  liquid,  or 
gaseous,  which  is  itself  injurious  to  health  or  which  may 
become  so  in  contact  with  other  substances,  whether  the 
latter  may  be  in  themselves  hurtful  or  not;  further,  any 
matter  which,  though  not  demonstrably  poisonous,  is  offen- 
sive to  the  senses."  (Slater,  "  Sewage  Treatment,  Purifica- 
tion, and  Utilization.")  Such  disposition  of  any  matter  that 
it  may,  while  in  the  condition  above  described,  approach 
within  effective  distance  of  any  dwelling  or  occupied  land 
should  be  held  to  be  a  nuisance.  A  recent  ruling  in  the 
United  States  has  included  in  the  "  creating  of  a  nuisance  " 
the  rendering  unfit  for  drinking  purposes  water  which  would 
otherwise  be  used  thus.  It  is  advisable  both  to  consult  the 
State  Board  of  Health  and  to  obtain  reliable  legal  advice 
before  deciding  finally  the  question  of  disposal. 


2O  SEWERAGE. 

With  these  principles  in  mind  a  thorough  and  intelligent 
study  of  the  local  conditions  should  be  made  to  decide  how 
the  requirements  of  sanitation  and  of  law  may  best  be  met; 
whether  any  treatment  of  the  sewage  will  be  necessary,  and 
if  so  which  is  best  adapted  to  the  given  conditions. 

ART.  11.    DISCHARGING  INTO  RIVERS  AND  TIDAL  WATERS. 

The  simplest  solution  of  the  problem,  where  it  is  permis- 
sible, and  the  one  most  frequently  employed  in  this  country, 
is  to  discharge  the  sewage  directly  into  some  flowing  stream 
or  large  body  of  fresh  water,  the  ocean  or  one  of  its  estuaries. 
This  is  called  "  disposal  by  dilution.'*  So  far  as  cheapness 
is  concerned  this  stands  easily  first  among  the  methods  of  dis- 
posal, since  it  requires  the  purchase  of  no  land  and  needs  no 
care  to  regulate  its  working,  excepting  where  the  discharge 
is  into  tidal  waters,  when  some  expense  is  frequently  gone 
to,  both  of  first  cost  and  of  maintenance,  to  regulate  the  time 
of  discharge.  It  is  usually  efficient  also  in  removing  the 
sewage  beyond  the  limits  of  the  area  contributing  to  its 
volume.  Looked  at  in  a  less  selfish  way,  and  considering  the 
good  of  the  State  and  country  as  well  as  of  the  locality 
sewered,  other  and  adverse  arguments  present  themselves. 
Although  the  sewage  is  removed  to  a  distance  from  the  con- 
tributing territory  by  tides  or  currents,  it  may  be  deposited 
in  proximity  to  other  communities,  on  banks  or  shores  or 
retained  by  dams,  thus  creating  a  nuisance;  or  may  render 
unfit  for  drinking,  household,  or  manufacturing  purposes 
water  which  would  otherwise  be  so  used.  Under  properly 
prepared  State  laws  such  interference  with  the  health  and 
rights  of  others  should  be  preventable  by  injunction,  or  in 
the  case  of  injury  to  manufacturing  interests  should  subject 
the  city  to  forfeiture  of  damages.  An  interesting  case 
under  the  latter  head  is  that  decided  in  1898  against 


SEWAGE   DISPOSAL.  21 

(Greater)  New  York  City  and  in  favor  of  an  oysterman  whose 
beds  were  destroyed  by  the  discharge  from  a  near-by  sewer- 
outlet  and  who  was  awarded  their  value  in  damages. 

In  this  connection  reference  should  be  made  to  the  danger 
of  spreading  certain  diseases  through  the  agency  of  oysters, 
and  that  of  the  destruction  of  fish  by  sewage  disposed  of  by 
dilution.  There  seems  to  be  little  doubt  that  typhoid  and 
probably  other  fevers  have  been  so  conveyed  by  osyters,  as  at 
Brightlingsea,  England,  oysters  from  which  place  were  accused 
on  good  evidence  of  having  caused  twenty-six  cases  of 
typhoid  fever  in  1897.  These  were  exposed,  however,  to 
-contact  for  hours  at  a  time,  at  low  tide,  with  sewage  but  little 
diluted.  In  view  of  this  and  of  similar  cases  both  in  this 
country  and  abroad  it  would  seem  advisable  that  precautions 
be  taken  by  the  authorities  to  protect  oyster-beds  from 
sewage  or  prevent  the  gathering  of  oysters  from  sewage- 
contaminated  waters. 

It  is  probable  that  germs  of  enteric  diseases  are  conveyed 
on  the  outside  rather  than  the  inside  of  the  body  of  the 
oyster,  and  that  there  is  little  danger  in  eating  sewage-fed 
fish  or  cooked  shellfish.  The  health  of  fish  does  not  neces- 
sarily suffer  from  sewage  pollution  of  the  waters  they  occupy, 
but  on  the  contrary  a  moderate  pollution  by  organic  matter 
seems  to  favor  their  growth.  (Acids,  dye-house  wastes,  etc., 
are  fatal  to  them,  however.)  Within  a  few  feet  of  an  outlet 
in  Boston  harbor  from  which  about  40,000,000  gallons  of 
sewage  daily  has  been  flowing  for  three  years  crabs  and 
bivalves  have  been  and  are  apparently  thriving.  There  seems 
no  reason  to  fear  that  organic  sewage,  if  well  diluted,  will 
exterminate  fish  life  from  a  river;  in  fact  it  is  much  less 
harmful  to  this  than  the  effluent  from  many  a  sewage  dis- 
posal works  employing  chemicals. 

It   is  still  a  mooted  question  to  what   extent  sewage  is 
rendered  innocuous  by  dilution  in  a  flowing  stream,  and  for 


22  SEWERAGE. 

how  great  a  distance  such  a  stream  continues  objectionably 
impure.  Such  changes  as  take  place  in  the  stream  are  due 
to  dilution  and  sedimentation,  a  slow  oxidation,  and  •  to  a 
certain  extent  a  consumption  of  the  sewage  matter  by  fish 
and  lower  forms  of  animal  and  vegetable  life.  Sewage  has 
been  traced  in  the  water  of  a  river  for  scores  of  miles  below 
the  point  of  its  discharge;  and  instances  are  recorded  where 
analyses  of  water  taken  at  intervals  of  several  miles  showed 
practically  no  disappearance  of  the  harmful  organic  matter, 
but  only  increased  dilution.  Also,  since  typhoid  germs  have 
been  known  to  live  in  ice-water  for  twenty-five  days,  it  is 
argued  that  the  water  of  a  river  receiving  sewage  is  dangerous 
for  use  as  drinking-water  for  a  distance  below  the  sewer- 
mouth  covered  by  the  flow  of  the  river  during  at  least  twenty- 
five  days,  or  say  six  hundred  miles. 

Basing  their  conclusions  on  such  arguments,  some  sani- 
tarians maintain  that  house-sewage  should  never,  or  only  in 
very  exceptional  cases,  be  discharged  into  a  stream  or  lake. 
The  arguments  in  favor  of  their  standpoint  are  certainly 
weighty,  but  on  the  other  hand  the  cost  of  treatment  is  con- 
siderable, and  many  towns  could  not  afford  a  sewerage  system 
at  all  if  a  plant  for  treatment  also  were  necessary.  A  balance 
of  benefits  and  evils,  of  what  is  desirable  and  what  is  possible, 
must  be  made  for  each  case.  "  A  question  which  we  should 
be  glad  to  have  answered  is  this:  To  what  extent  must  a 
polluted  liquid  be  diluted  in  order  to  be  safely  used  for 
domestic  purposes?  The  answer,  however,  none  can  give. 
We  do  know  this:  it  has  been  shown  by  actual  experiment 
that  the  spores  of  some  of  the  lower  orders  of  vegetable 
organisms  are  very  difficult  to  deprive  of  vitality;  they  may 
be  frozen  or  heated  to  the  boiling  temperature,  or  they  may 
be  kept  in  a  dry  condition  for  years,  and  then,  if  placed  in  a 
favorable  medium,  become  active  and  produce  their  kind. 
Admitting  the  presence  of  disease-germs  in  a  liquid,  the 


SEWAGE  DISPOSAL.  2$ 

liquid  may  be  diluted  until  the  chance  of  taking  even  a  single 
germ  into  the  system  is  so  small  that  it  may  be  disregarded; 
and  yet  if  the  prevailing  theory  be  true  a  single  germ  if 
taken  might  produce  disastrous  results.  It  is  easy  to  push 
the  demands  for  purity  to  an  absurd  extent;  all  reasonable 
precautions  should  be  taken  to  insure  purity,  but  there  is  a 
point  beyond  which  it  is  foolish  to  attempt  to  go.  In  the 
present  state  of  our  knowledge  we  should,  however,  err  on 
the  side  of  safety,  and  the  mere  fact  that  chemical  analysis 
fails  to  detect  impurity  should  not  be  accepted  as  a  guaranty 
-that  a  water  is  fit  to  drink."  (Nichols,  "  Water  Supply, 
Chemical  and  Sanitary.") 

"  The  minute  forms  of  animal  life  are  thus  seen  to  be 
powerful  agents  in  the  self-purification  of  sewage-polluted 
water,  but  the  conclusion  which  has  been  drawn,  that  there- 
fore sewage-polluted  streams  are  after  a  few  miles'  flow  fitted 
through  the  action  of  such  and  other  natural  agencies  for 
drinking,  is  not  wholly  justified  by  the  present  state  of  knowl- 
edge of  the  subject  as  a  whole. 

"  Along  with  our  knowledge  of  the  purifying  action  of  the 
minute  animals  and  plants  has  grown  up  a  more  definite 
knowledge  of  the  causation  of  typhoid  fever,  cholera,  and  the 
other  water-borne  communicable  diseases;  and  before  it  can 
be  positively  affirmed  that  a  sewage-polluted  stream  is  safe 
for  drinking  after  a  few  miles'  flow  it  must  be  shown  so 
definitely  as  to  be  beyond  question  by  those  whose  special 
studies  have  fitted  them  for  intelligent  judgment  that  the 
purifying  agencies  have  practically  eliminated  the  germs  of 
the  water-borne  communicable  diseases.  Until  such  showing 
is  clearly  made  the  proposition  that  crude  sewage  ought  not 
to  be  turned  into  running  streams,  ponds,  lakes,  or  other 
bodies  of  water  which  either  are  or  may  be  the  sources  of 
water-supplies  must  be  considered  as  holding  good."  (Rafter 
and  Baker,  "  Sewage  Disposal  in  the  United  States.") 


24  SEWERAGE. 

The  above  restrictions  apply  equally  to  ice  which  may  be 
used  for  drinking-water,  since  it  is  known  that  bacteria  are 
not  excluded  from  water  by  freezing  and  that  many  varieties 
will  live  in  ice  for  months. 

Apart  from  the  danger  of  communicating  disease  by 
sewage  pollution  of  water  is  that  of  causing  a  nuisance  by  so 
considerable  a  pollution  that  the  combined  action  of  dilution, 
oxidation,  and  consumption  by  animal  and  vegetable  life  is 
not  sufficient  to  prevent  a  considerable  sedimentation,  fol- 
lowed by  nocuous  decomposition  or  objectionable  minor 
evidences  of  the  impurity  of  the  water.  Dilution  is  largely 
an  expedient  for  facilitating  oxidation,  and  hence  the  greater 
the  amount  of  oxygen  in  a  body  of  water  the  more  sewage 
can  it  assimilate,  both  because  of  the  greater  possibilities  of 
oxidation  and  because  of  the  greater  quantity  of  animal  life 
present  which  will  assist  in  the  purification.  A  stream  with 
a  rapid,  agitated  flow  may  be  charged  with  a  greater  per- 
centage of  sewage  than  a  sluggish  one,  both  because  of  the 
greater  amount  of  oxygen  and  because  the  mixture  of  the 
sewage  and  water  becomes  more  thorough.  Sewage  dis- 
charged into  a  slow  current  can  often  be  traced  for  a  long 
distance  as  a  separate  stream,  mingling  but  slowly  and  along 
its  edges  with  the  purer  water.  A  slow  current  will  also 
favor  deposits  of  the  heavier  sewage  matter.  For  these 
reasons  the  point  of  most  rapid  flow  of  stream  or  current 
should  be  chosen  for  the  outlet. 

Authorities  differ  as  to  the  minimum  amount  of  dilution 
necessary,  but  this  is  usually  placed  between  1500  and  3500 
gallons  per  day  per  person  contributing  to  the  sewage.  The 
proportion  is  sometimes  stated  in  terms  of  cubic  feet  of 
sewage,  but,  since  the  amount  of  impurity  is  not  increased  by 
greater  per  capita  consumption  or  waste  of  water,  the  former 
method  seems  preferable. 

In  a  few  States  sewerage  systems  must  be  so  designed, 


before  meeting  the  approval  of  the  State  Boards  of  Health, 
as  to  permit  and  provide  for  a  treatment  of  the  house-sewage 
at  some  future  time,  although  temporarily  they  may  be 
allowed  to  discharge  into  adjacent  streams.  It  is  probable 
that  before  very  long  this  will  be  the  regulation  in  most 
States.  But  in  any  event  where  the  discharge  is  into  a 
stream  or  lake  the  possibility  of  the  necessity  arising  in  the 
future  for  treatment  of  the  sewage  should  be  foreseen  and 
provided  for  in  the  design  of  the  system. 

The  discharging  of  sewage  into  tidal  waters  involves  the 
principles  given  as  applying  to  discharge  into  rivers  so  far  as 
creating  a  nuisance  is  concerned,  and  also  the  practical  con- 
sideration of  the  movements  of  prevailing  winds  and  tides. 
That  is,  such  a  location,  time,  and  method  of  discharge  must 
be  selected  as  will  insure  the  sewage  being  carried  away  from 
the  shore.  Discharging  into  a  landlocked  bay  or  during  a 
flood  tide  will  not  insure  this.  An  illustration  of  the  former 
error  is  the  city  of  Havana,  Cuba,  which  discharges  its  sewage 
into  a  harbor  almost  surrounded  by  land  and  where  tides  have 
but  little  effect.  Partially,  at  least,  from  this  cause  it  results, 
as  one  of  her  citizens  has  stated,  that  Havana  is  "  the  most 
intense  focus  of  yellow  fever  in  the  world."  "  In  every  case 
the  outfall  of  the  discharging  sewer  should  be  below  the  level 
of  the  water  at  all  states  of  the  tide,  and  be  provided  with  a 
tidal  valve,  to  prevent  the  ingress  of  sea-water.  The  position 
of  the  outfall  should,  if  possible,  be  so  chosen  that  the  sewage 
will  be  always  carried  out  to  sea  independently  of  the  tides 
and  the  possibility  of  its  return  avoided;  and  for  this  purpose 
advantage  should  be  taken  of  any  current  that  flows  off  or 
along  the  shore,  the  sewage  being  discharged  into  it,  and  thus 
•carried  away  from  the  neighborhood  of  the  town.  If  there 
is  a  current  setting  along  the  shore,  then  the  sewer  outfall 
should  be  placed  at  that  extremity  of  the  town  which  will 
prevent  the  sewage  being  borne  along  the  whole  sea  front. 


26  SEWERAGE. 

The  prevailing  winds  must  also  be  taken  into  account,  so  that 
floating  matters  may  not  be  blown  back  toward  the  town.'* 
(W.  H.  Corfield,  "  Treatment  and  Utilization  of  Sewage.") 

The  desired  result  may  usually  be  obtained  by  discharging 
into  an  ebbing  tide  only.  In  general  also  it  may  be  said 
that  the  deeper  the  outlet  of  the  sewer  the  less  the  proba- 
bility of  floating  matter  being  blown  upon  the  shore,  because 
the  greater  its  comminution. 

ART.  12.     SEWAGE  TREATMENT. 

In  many  inland  cities  no  streams  of  sufficient  size  are 
available  as  outlets  for  the  sewers,  and  these,  as  well  as  those 
which  for  other  reasons  do  not  adopt  dilution  as  the  method 
of  disposal,  must  needs  treat  their  sewage  in  some  way.  The 
methods  of  disposal  coming  under  the  head  of  treatment  can 
be  generally  classified  as  oxidation  by  land  and  by  fire  and 
precipitation  by  chemicals. 

The  chemicals  most  commonly  used  are  lime  and  sulphate 
of  alumina,  which  are  mixed  with  the  raw  sewage.  The 
object  of  their  use  is  to  separate  the  impurities  from  the 
water  and  thus  render  them  more  easily  dealt  with.  A  part 
only,  though  in  some  cases  a  large  part,  of  the  impurities  are 
thus  removed.  Chemical  precipitation  involves  the  use 
finally  of  either  earth  or  fire;  for  it  but  removes  and  does  not 
destroy  the  objectionable  matter,  which  must  still  in  its  more 
condensed  form  be  disposed  of. 

Chemical  precipitation  is  sometimes  employed  as  a  pre- 
liminary to  land  treatment,  especially  where  the  amount  of 
land  available  is  limited.  In  many  cases  no  further  treatment 
is  given  the  effluent;  but  if  additional  purification  is  neces- 
sary a  much  less  area  of  land  is  required  for  treating  the 
effluent  than  would  be  needed  to  treat  the  raw  sewage. 
Chemical  treatment  is  therefore  particularly  applicable  to 


SEWAGE   DISPOSAL.  2/ 

localities  where  sufficient  land  for  filtration  or  irrigation  is 
unattainable  or  prohibitively  expensive. 

The  matter  precipitated  is  usually  compressed  into 
"  sludge-cakes,"  which  are  sold  for  fertilizer  if  possible;  other- 
wise they  are  disposed  of  on  land  or  burned  in  a  cremator. 

During  the  last  few  years  another  method  of  treating 
sewage  has  come  into  prominence  under  the  name  of  the 
septic  tank  treatment.  In  this  the  structure  of  many  organic 
matters  is  broken  down  and  resolved  into  carbonic  acid  and 
other  gases,  ammonia  and  other  nitrogenous  compounds,  in 
the  almost  total  absence  of  oxygen,  the  gases  being  allowed 
to  escape,  while  the  effluent  is  in  a  condition  more  readily 
susceptible  to  rapid  purification  or  dilution.  Sufficient  data 
have  not  yet  (1898)  been  collected  to  demonstrate  the  value 
of  this  method  nor  its  economy  when  used  upon  a  large  scale. 

The  treatment  with  earth  includes  all  use  of  the  sewage  as 
a  fertilizer,  whether  in  its  crude  state  or  in  the  shape  of 
poudrette.  Excrement  removed  by  the  Pail  and  Dry-earth 
systems  is  usually  spread  as  a  fertilizer  upon  land.  This  is 
commonly  done  by  ploughing  furrows  about  two  feet  apart, 
depositing  the  matter  in  them,  and  turning  the  mould  upon 
it  by  intermediate  furrows.  Two  such  applications,  in  the 
spring  and  fall,  are  all  that  most  lands  will  receive  to  advan- 
tage. The  sludge  produced  by  chemical  precipitation  is  fre- 
quently used  as  fertilizer,  or  even,  when  it  cannot  otherwise 
be  gotten  rid  of,  is  buried  in  cakes  a  few  feet  under  the 
surface  of  the  ground. 

The  most  common  use  of  earth,  however,  is  in  the  treat- 
ment of  sewage  by  irrigation  and  by  filtration.  The  examples 
of  this  use  of  land  are  already  numbered  by  the  hundreds, 
with  the  list  being  constantly  swelled.  In  these  the  sewage 
from  the  water-carriage  system  is  turned  upon  the  land,  and 
passes  downward  through  it,  the  effluent  being  usually  inter- 
cepted by  drains  and  conducted  to  a  neighboring  water- 


28  SEWERAGE. 

course.  During  its  transit  the  sewage  is  purified  by  oxidation 
of  its  organic  constituents,  the  agent  thereof  being  the  air 
contained  in  the  interstices  of  the  soil,  assisted  by  certain 
bacteria.  A  very  large  percentage  of  the  disease-germs  present 
are  usually  removed  at  the  same  time.  If  vegetable  growth 
of  some  kind  is  raised  upon  this  land  the  method  is  called 
irrigation;  if  the  land  is  kept  clear,  in  which  case  more  sewage 
can  be  treated  on  a  given  area,  the  process  is  called  filtration. 
A  porous  soil  is  that  best  adapted  to  this  treatment,  though 
many  fairly  successful  systems  are  in  operation  on  somewhat 
clayey  or  boggy  soil. 

Where  suitable  soil  is  not  obtainable  or  is  expensive  coke- 
breeze  or  similar  coarse  material  may  be  used  to  advantage, 
not  more  than  one  tenth  the  area  required  by  sand  filtration 
being  necessary  to  obtain  equal  results,  judging  by  recent 
experiments.  Both  sand  and  coke-breeze  filtration  are  filtra- 
tion in  only  a  limited  degree,  and  these  filters  are  by  some 
called  "  bacteria-tanks,"  by  others  "  biological  filters." 

Disposal  t^v_fire,  or  incineration,  is  used  for  the  destruc- 
tion of  house-sewage  or  of  cakes  of  sludge.  Cremators 
similar  to  those  used  for  garbage  destruction  are  excellently 
well  adapted  to  this  purpose;  in  fact  where  large  amounts  of 
sewage  are  to  be  disposed  of  by  incineration  some  such 
furnace,  which  will  consume  its  own  gases,  is  necessary  (see 
also  Art.  3). 

For  details  concerning  the  various  methods  of  treatment 
above  mentioned  the  works  previously  referred  to  are  recom- 
mended. If  treatment  is  necessary  the  planning  of  the  same 
should  be  made  a  special  study ;  and  the  cases  are  few  indeed 
where  some  provision  for  future,  if  not  for  immediate,  treat- 
ment is  not  imperatively  demanded.  The  designing  engineer 
should  hesitate  long  before  adopting  as  a  final  solution  of  the 
question  the  method  of  simple  dilution.  In  general  it  may 
be  said,  however,  that  this  is  temporarily  permissible  when 


SEWAGE  DISPOSAL.  2$ 

the  water  of  dilution  is  not  used  as  a  beverage  by  any 
community  within  20  to  50  miles  down  stream  from  the 
sewer-outlet,  and  provided  that  a  dilution  at  least  equal  to 
that  given  in  Art.  1 1  is  immediately  obtained,  and  that  the 
current  is  of  proper  strength  and  direction  to  prevent  deposits. 


CHAPTER    III. 
AMOUNT   OF   SEWAGE. 

ART.  13.     SEWERAGE   CONDUITS. 

THE  object  of  a  system  of  sewers  is  in  general  to  conduct 
all  excreta  and  fouled  waters  from  the  places  of  their  origin 
to  an  appointed  outlet,  and  as  rapidly  and  continuously  as 
possible.  No  part  of  the  sewage  should  be  retained  in  any 
portion  of  the  system  for  any  considerable  time,  either  in  its 
liquid  form  or  in  the  shape  of  deposits  upon  the  bottoms  or 
walls  of  the  conduits  or  their  appurtenances;  for  such  reten- 
tion may  permit  of  putrescence  of  the  organic  matter  before 
it  reaches  the  place  assigned  for  disposal,  the  conduits  thus 
becoming  no  better  than  *'  elongated  cesspools."  The  insur- 
ing of  this  result  with  the  greatest  certainty  and  economy  is- 
the  prime  requisite  in  the  design  of  a  sewerage  system. 

The  largest  part  of  the  system  is  made  up  of  conduits  of 
various  size,  shape,  grade,  material,  and  depth  below  the 
ground-surface.  The  two  last  are  practical  points  to  be  con- 
sidered later  (Articles  37  and  45),  but  the  size,  shape,  and 
grade  are  to  be  determined — approximately  at  least — by 
theoretical  considerations.  The  data  used  in  these  considera- 
tions are  (i)  the  amount  and  character  of  the  sewage  to  be 
removed,  and  (2)  the  relative  surface  elevations  and  grades 
along  the  line  of  the  proposed  sewer-conduit.  The  latter 
are  obtained  by  the  instrumental  field-work,  to  be  discussed 
in  Chapter  VI.  While  the  grade  of  the  sewer  need  not  be 

30 


AMOUNT  OF  SEWAGE.  3 1 

that  of  the  street-surface,  it  cannot  depart  far  from  this  with- 
out greatly  increasing  the  difficulty  and  cost  of  construction. 
The  two  grades  will  therefore  be  approximately  parallel 
unless  very  good  reasons  to  the  contrary  exist. 

ART.  14.    AMOUNT  OF  HOUSE-SEWAGE. 

The  obtaining  of  satisfactory  figures  for  the  amount  of 
sewage  is  one  of  the  most  difficult  tasks  entering  into  the 
designing  of  a  system.  The  sewage  to  be  considered  is  of 
two  entirely  different  kinds,  from  two  totally  different 
sources:  house-sewage  from  dwellings,  stores,  factories,  and 
other  buildings,  and  storm-water  from  the  streets,  the  ground- 
surface,  and  from  roofs.  The  former  is  limited  in  quantity 
largely  by  the  number  of  inhabitants  and  industrial  establish- 
ments and  the  water  contributed  to  the  sewers  by  each. 
The  latter  is  limited  by  nature's  local  limit  of  intensity  of 
rainfall,  the  area  tributary  to  the  sewer,  and  the  proportional 
run-off. 

Considering  first  the  house-sewage,  this  is  almost  entirely 
composed  of  water  which  has  first  been  introduced  artificially 
into  the  dwellings  or  establishments.  Excreta  and  solids 
legitimately  finding  their  way  to  the  sewer  comprise  only  a 
very  small  part  of  the  sewage — from  5  to  15  parts  in  10,000. 
There  may  be  besides  this  comparatively  small  amounts  of 
leakage  of  ground-water,  roof-water,  and  flushing-water 
reaching  the  sewer.  It  would  seem,  therefore,  that  we  may 
make  a  close  approximation  to  the  amount  of  house-sewage 
by  using  the  water-consumption  of  the  town  in  question. 
This  can  usually  be  obtained  from  the  pumping  records,  or, 
in  the  case  of  a  gravity  supply,  from  a  meter  set  in  the  main 
near  the  reservoir.  Table  No.  I  shows  the  rates  for  a  num- 
ber of  cities  of  the  United  States  at  intervals  of  10  years. 
This  table  shows  the  great  difference  between  the  per  capita 


32 


SEWERAGE. 
TABLE  No.  1. 


1870. 

1880. 

1890 

Cities. 

Population. 

Per  Capita 
Consumption. 

Population. 

Per  Capita 
Consumption. 

Population. 

Per  Capita 
Consumption. 

New  York  City     • 

Q42  2Q2 

no  2 

I  206  5QO 

78  7 

I     ETC     <1OI 

7o 

Chicago,  111  

2q8,Q77 

62.^2 

503,  304 

TI4.O 

I   OQQ   8^O 

/y 

138 

Philadelphia.  Pa  
Brooklyn    N.  Y  

674,022 

•306  OQQ 

55-11 
47  l6 

847,542 
566  680 

68.1 

C.A     2 

1,046,964 
806   34^ 

131 

72 

St    Louis    Mo  

310,864 

qe   og 

046  ooo 

72  I 

451    7  7O 

72 

2^0,526 

60.  1  5 

416,000 

Q2  O 

•     448  477 

80 

216,236 

40  o 

256,708 

7q  Q 

206  008 

112 

Cleveland    O 

Q2  82Q 

•70  24 

65  o 

261    ^^7 

IO1 

Buffalo    NY    

117  714 

58  08 

106  o 

oce  664 

1  86 

Detroit    Mich  

7Q  577 

64.  24 

118  ooo 

I52O 

205  876 

161 

IOO  753 

2Q  O 

C2  o 

l6l    I2Q 

74. 

88  150 

78 

78  347 

128 

Fall  River,  Mass  

40.  43O 

3O  I 

74  ^08 

2O 

70,028 

64 

Troy,  N.  Y  

60,056 

125 

5O.OQ3 

e.e. 

Erie   Pa    

4O  634 

112 

. 

3O  217 

83 

2O  056 

22 

San  Jose   Cal  

1  8  060 

IQ4 

Keokuk,  la  

I4,IOI 

78 

I2,IO3 

73 

10  478 

iq 

IO  O44 

IQQ 

rates  in  different  cities.  It  also  shows  in  each  city  an  increase 
of  from  10%  to  100%  in  consumption  during  each  decade. 
Neither  the  increase  of  per  capita  consumption  nor  the  dif- 
ference in  rates  of  increase  in  the  various  cities  seems  to 
follow  any  law,  except  that  the  former  shows  a  constant 
advance.  It  might  be  expected  that  the  per  capita  con- 
sumption would  be  greater  in  cities  where  there  was  consider- 
able manufacturing  or  many  well-kept  lawns  than  where  these 
conditions  did  not  exist;  and  this  is  the  general  rule — with 
many  exceptions,  however.  Also  large  cities  usually  have  a 
higher  rate  than  small  ones;  but  this  rule  also  has  many 
exceptions. 


AMOUNT  OF  SEWAGE.  33 

For  each  particular  case  the  daily  consumption  should  be 
obtained  from  the  water-works  record,  or,  if  there  are  no 
records  of  consumption  for  that  locality,  a  careful  selection 
should  be  made  of  the  per  capita  consumption  of  a  city  whose 
conditions  closely  resemble  those  of  the  place  in  question. 
From  these  the  per  capita  rate  will  be  obtained.  In  order  to 
be  on  the  safe  side  the  present  rate  should  be  increased  by  at 
least  25$  to  allow  for  a  probable  increase  in  consumption, 
since  the  construction  must  serve  not  only  the  present  popu- 
lation, but  that  of  the  next  30  or  more  years. 

If  meters  are  used  on  a  majority  of  the  services  a  great 
reduction  in  the  consumption  can  be  effected — from  30$  to 
60$  in  most  instances. 

Unless  water-meters  have  become  generally  established 
and  accepted,  however,  no  allowance  should  be  made  for  the 
reduction  in  sewage  due  to  their  use  unless  the  average  daily 
rate  exceeds  100  gallons  per  capita.  There  is  no  reason  for 
a  daily  rate  exceeding  this  amount,  and  the  present  tendency 
is  to  meter  supplies  before  they  reach  this  point.  An  allow- 
ance of  100  gallons  will  be  made  in  calculations  in  this  work, 
as  being  a  safe  one  for  any  but  exceptional  cases. 

The  average  daily  consumption,  however,  "  is  not  uniform 
throughout  the  year,  but  at  times  is  greatly  in  excess  of  the 
average  for  the  year  and  at  other  times  falls  below  it.  It 
may  be  20$  or  30$  in  excess  during  several  consecutive 
weeks,  50$  during  several  consecutive  days,  and  not  infre- 
quently loofo  in  excess  during  several  consecutive  hours." 
(J.  T.  Fanning,  "  Water  Supply  Engineering.")  Many  water- 
works engineers  use  75$  excess  as  an  average.  This  gives 
for  a  maximum  flow,  on  a  basis  of  100  gallons  daily,  a  rate 
of  175  gallons  per  capita  daily  =  .1215  gallons  per  minute  = 
.00027  cubic  feet  per  second. 

It  must  be  most  urgently  insisted,  however,  that  each  case 
should  be  studied  by  itself  in  the  light  of  all  the  data  avail- 


34  SEWERAGE. 

able.  These  figures  are  given  as  approximate  averages  only, 
to  be  used  in  designing  when  no  local  records  exist.  It 
should  also  be  borne  in  mind  that  the  consumption  given  is 
an  average  including  that  used  in  manufacturing  and  for  all 
other  purposes.  These  last  constitute  a  very  uncertain  por- 
tion of  the  whole,  but  unless  there  were  definite  figures 
obtainable  it  would  not  be  safe  to  reduce  the  average  by 
more  than  10$  to  obtain  a  rate  for  residences  only.  As  the 
assumed  maximum  rate — 175  gallons — was  but  a  roughly 
estimated  average,  it  may  be  used  unchanged  for  residential 
districts ;  and  where  factories  are  to  be  provided  for  a  study 
should  be  made  of  the  processes  employed  in  them  in  order 
that  a  close  approximation  may  be  made  to  the  amount  of 
sewage  to  be  expected  from  each. 

The  amount  of  house-sewage  from  buildings  (other  than 
waste  water  from  factories  and  water-motors)  which  will  reach 
any  particular  sewer  will  depend  almost  wholly  upon  the 
number  of  persons  contributing  to  this  amount.  For  a 
district  or  city  this  number  may  be  obtained  in  two  ways 
— by  estimating  the  ultimate  number  of  residences  and 
assigning  a  certain  number  of  occupants  to  each,  doing  the 
same  with  factories,  stores,  and  other  buildings;  or  by 
estimating  the  probable  ultimate  population  per  acre  for 
different  sections  of  the  city.  The  former  is  the  more  accu- 
rate for  built-up  sections;  the  latter  sufficiently  so  for 
undeveloped  territory  or  that  which  will  probably  undergo  a 
change  in  the  character  of  its  buildings. 

For  use  in  calculating  by  the  first  method  the  following 
table  adapted  from  the  U.  S.  census  of  1880  is  given. 

There  are  in  each  city  certain  districts  in  which  the 
population  is  much  more  dense  than  is  indicated  by  this 
table.  One  hundred  persons  in  one  dwelling  is  not  an  excep- 
tional rate  in  certain  portions  of  New  York  City.  For  an 
ordinary  residence  district  six  persons  to  each  dwelling  is  a 


AMOUNT  OF  SEW  A 
TABLE  No.  2. 


Cities. 

Population. 

Persons  in  a 
Family. 

Persons  in  a 
Dwelling. 

New  York  City         

I  206  299 

406 

16  77 

New  Orleans    La  

216  090 

477 

5QC 

lO-i-S^? 

A    C2 

7  J.I 

ec,  785 

C.Q7 

6  d8 

43,350 

C.OQ 

6.iq 

75,620 

C.QQ 

6  7«? 

qo  762 

4.  78 

e   16 

Erie    Pa     .          

27,737 

c.24 

*  66 

22,4O8 

5.14 

e    -27 

2I,42O 

4.51 

c  O7 

Springfield     111    

IQ    74.-I 

e.o4 

*  60 

sufficient  average.  In  factories  and  stores  which  do  not  use 
water  for  manufacturing  purposes  the  maximum  hourly  rate 
per  capita  of  occupants  is  not  nearly  as  great  as  in  the  case  of 
residences;  a  maximum  rate  of  20  gallons  per  day  will  be 
sufficient  allowance  for  ordinary  cases,  being  contributed  by 
water-closet  flushes,  urinals,  and  wash-basins.  '  One  person 
to  each  50  square  feet  of  floor-space  may  be  taken  as  a 
maximum  density  for  factories,  and  one  to  each  75  square 
feet  for  office-buildings. 

A  method  frequently  used  is  that  of  adding  a  percentage 
of  increase  to  the  present  population  of  each  city  or  section. 
American  towns  under  50,000  population  have  been  found  as 
a  general  rule  to  double  in  size  in  about  15  or  20  years. 
Having  ascertained  for  each  case  its  past  rate  of  increase  and 
present  population,  these  are  taken  as  the  basis  for  calcula- 
tions. But  this  increase  is  far  from  uniform  over  the  entire 
area  of  a  town,  differing  in  different  sections;  also  after  a 
section  has  reached  a  certain  density  of  population  it  remains 
practically  stationary,  unless  its  character  change — as  from 
residential  to  business  or  manufacturing.  The  percentage  of 
total  growth  of  a  town  may  be  used,  however,  as  a  check 
upon  the  sum  of  the  populations  assumed  for  the  various  sec- 
tions. The  law  of  increase  varies  in  different  cities,  but  that 


36  SEWERAGE. 

followed  in  the  past  by  the  one  under  consideration  having 
been  obtained  from  the  records  can  be  projected  into  the 
future,  it  being  assumed  that  this  law  will  remain  constant 
(see  Art.  129). 

Considerable  judgment  must  be  used  in  locating  division- 
lines  between  sections  and  assigning  to  each  its  density  of 
ultimate  population.  The  most  hilly  sections  will  probably 
be  least  thickly,  and  those  in  the  level  bottom  lands  most 
thickly,  populated.  Further  than  this  it  would  be  unsafe  to 
try  to  state  any  general  law.  The  least  population  which 
should  be  assigned  to  any  habitable  section  within  city  limits 
is  20  per  acre.  The  per  acre  population  in  any  residence 
section  can  be  expressed  by  the  equation 

4356o/fo 

-  fd\lb  +  w(l  +  b  +  w)y 

in  which  /  =  the  average  length  of  a  city  block ; 

b=    "        "        breadth "  "    "       " 

o  —    "  number  of  occupants  of  each  lot; 

/=    "        "  *        "    front  feet  to  a  lot; 

d=    "        4<        depth  of  a  lot; 

w=    "         "        width  of  a  street; 

P  •=.    "  population  per  acre. 

For  a  section  where  the  blocks  are  400  ft.  by  200  ft.y 
streets  66  ft.  wide,  lots  50  ft.  by  100  ft.,  and  the  population 
residential  (o  =  6), 

43560  X  4QQ  X  200  X  6 

"  50  X  ioo[400  X  200  +  66(400  +  200  +  66)]  ~ 

For  a  tenement  district,  each  building  on  a  lot  50  ft.  by 
100  ft.  and  containing  on  an  average  80  occupants,  P  would 
equal  453,  which  is  about  P  for  the  Tenth  Ward,  New  York 
City. 

A  block  with  lots  25  feet  by  80  feet  and  with  6  occu- 
pants each  represents  fairly  well  the  most  dense  residence 


AMOUNT  OF  SEWAGE.  37 

section  of  an  average  city  of  10,000  to  100,000  population. 
This  gives  P=  85.  In  many  cities  the  maximum  does  not 
exceed  50  per  acre. 

The  population  found  times  .00027  f°r  residences  and 
times  .00003  for  factories  and  office-buildings  (on  the  basis  of 
the  previously  assumed  daily  consumption)  will  give  in  cubic 
feet  per  second  the  maximum  amount  of  house-sewage  from 
buildings  to  be  expected.  To  this  must  be  added  manufac- 
turing wastes,  which  are  to  be  allowed  for  in  quantities  which 
must  be  decided  upon  separately  for  each  individual  case. 
Also  if  the  soil  is  inclined  to  be  wet  at  a  depth  less  than  that 
of  the  proposed  sewer  (and  this  includes  a  larger  proportion 
of  localities  than  most  persons  realize)  an  additional  allowance 
must  be  made  for  ground-water  leaking  through  the  joints 
(see  Art.  35).  With  care  this  need  not  amount  to  more  than 
one  cubic  foot  per  second  for  each  30  to  100  miles  of  sewer; 
but  it  has  been  known  under  most  unusual  conditions  to  more 
than  equal  the  entire  capacity  of  the  system. 

Where  flush-tanks  are  used  (see  Chapter  V)  an  additional 
allowance  is  frequently  made  for  water  from  them.  But  this 
seems  entirely  unnecessary,  since  their  very  purpose  is  to  tem- 
porarily gorge  the  sewer  for  as  great  a  distance  as  possible; 
and  the  smaller  the  sewer  the  better  is  this  mission  fulfilled. 
The  average  discharge  per  minute  of  100  tanks,  each  dis- 
charging 300  gallons  once  in  24  hours,  would  amount  to  only 
\\%  of  the  capacity  of  a  1 5-inch  sewer  at  minimum  grade. 

ART.  15.     DATA  OF  HOUSE-SEWAGE  FLOW. 

Instead  of  using  rates  of  water-consumption  as  equivalent 
to  the  sewage  discharge  it  would  undoubtedly  be  preferable 
to  establish  the  actual  relation  between  these,  based  upon  the 
rate  of  flow  of  sewage  itself  in  various  towns  already  sewered. 
But  very  few  such  records  exist — too  few  to  enable  us  to 
deduce  a  definite  law  from  them  with  certainty,  although  a 


SEWERAGE. 


study  of  even  these  few  is  instructive.  Probably  the  most 
extended  series  of  gaugings  of  sewage  discharge  made  in 
America  are  those  of  the  Providence,  R.  I.,  sewers  by 
Samuel  M.  Gray.  A  condensed  summary  of  them  and  of 
other  gaugings  is  given  in  the  following  tables: 

TABLE  No.  3. 

SUMMARY    OF    RESULTS    OF    WEIR      MEASUREMENTS    OF    SEWAGE    FLOW 

IN    PROVIDENCE,    R.    I. 
(Condensed  from  a  Report  by  SAMUEL  M.  GRAY  on  the  Sewerage  of  Providence.} 


Street. 

Houses 
Connected. 

Population 
Connected. 

Average 
Discharge 
per  Second. 

Maximum 
Discharge 
per  Second. 

Date  of 
Measurement. 

Dorrance  

772 

6562 

7.  -22 

1  1  65 

f  Average  of 

Brook  

C7C 

4.d8O 

c  02 

6  78 

}  May  and  June 
Sat.    Feb    2 

5.6l 

6  78 

Mon     "        4 

3.085 

c  47 

Xues  ,  Julv  I 

3-88 

5.47 

Thurs.,   "    3 

3-86 

5.76 

Sat.,         "     5 

4.28 

5.47 

Mon.,       '    7 

Elm     

III4 

8"8oo 

4.15 

7  QO 

"      Jan    28 

3  6q 

7  QO 

Xues       "     20 

«, 

7.^17 

6  32 

\Ved.    June  4 

« 

q.  37 

6  32 

Fri.,         "     6 

i  t 

3.IO 

c   ii 

Thurs.,    "     19 

N   Main  

2.57 

4.4< 

Mon  ,  May  12 

•  2.46 

T.SO 

Wed.,      "     7 

( 

1.76 

•2    25 

Fri.,  July  25 

I.  CQ 

3    2O 

Mon     Feb.  IT 

2  40 

5  4O 

Xhurs      "     14 

i 

2.3O 

4  82 

Sat.,         "    16 

< 

2.06 

2  65 

Mon.       "    18 

, 

2.IO6 

3  2O 

Fri.,         "    29 

2O4. 

1814 

O.753 

.02 

Mon.,  March  3 

0.854 

.38 

Wed.,      "       5 

«t 

O.6q5 

.30 

Mon.,  Aug.  25 

14 

o  600 

O  Q2 

Wed  ,      "      27 

College   

1  08 

824 

I.O5 

.82 

Fri.,  May  2 

I.  O7 

.81 

Mon.,  "        5 

Point  

•321 

2720 

1.57 

3.82 

(  Mean  for  May 

Power  

31 

23Q 

O.26 

o  56 

]        6-21 

Wed  ,  April  23 

O.26 

O.  54 

Fri.,         "      25 

« 

O.O45 

0.14 

"     Aug.  22 

Nash  

25 

IQ3 

O.O37 

0.  175 

Mon.,  April  21 

<« 

O.O3O 

O.O6O 

Tues.  ,      "     22 

ii 

O.O36 

O.O86 

Auef.  6,  7,  II 

Park       

2f 

162 

o  034 

o  187 

Fri.,  April  18 

« 

0.043 

0.^85 

Mon.,  Aug.  18 

Martin  

ica 

1178 

1.  208 

I.4OO 

Wed.,  Julv  9 

Pitman             . 

86 

655 

I.2O2 

2.38o 

Mon.,  April  28 

O.744 

I.38o 

Wed.,       "     30 

AMOUNT   OF  SEWAGE. 


39 


TABLE  No.  4. 

GAUGINGS    MADE    IN    TORONTO,    CANADA,    IN     THE     SPRING    OF    1891, 
LASTING    THREE    DAYS. 


Popula- 
tion per 
Acse. 

Total 
Popu- 
lation. 

Discharge. 
Gallons  per 
Head  per 
Day. 

Popula- 
tion per 
Acre. 

Total 
Popu- 
lation. 

Discharge. 
Gallons  per 
Head  per 
Day. 

Popula- 
tion per 
Acre. 

Total 
Popu- 
lation. 

Discharge. 
Gallons  per 
Head  per 
Day. 

15-7 
46.2 
8.8 
44.0 
45.5 

39,014 
17,186 
3,168 
572 
4,595 

77 
133 
83 
3I6* 

77 

I7.6 
42.3 
39-8 
42.4 
u.8 

6,160 
11,125 
6,368 

8,268 
8,732 

IOI 
69 

"3 

89 

IO2 

4L7 
9.4 

45-7 
38.3 
24.0 

11,300 
7,238 
14,213 
19,265 

68 
105 
89 

53 

87 

41.8 

1,045 

H3 

43-7 

9.832 

89 

*  No  explanation  given  for  this  high  average. 

TABLE  No.  5. 

GAUGINGS    MADE    IN  SCHENECTADY,  N.  Y.,  WEDNESDAY,  FEBRUARY  5, 

AND  THURSDAY,  FEBRUARY  6,  1892 — HOURLY  FOR  24  HOURS. 
(Fifteen  miles  of  sewers,  about  1500  house-connections  tributary  to  the  point 
where  gaugings  were  made.  Before  house-connections  were  made  a  seepage 
of  60,000  gallons  per  day  was  measured.  There  was  also  50,000  gallons  of 
water  contributed  daily  by  flush-tanks.  These  two,  or  110,000  gallons  per  day, 
have  been  deducted  from  the  total  hourly  flow  in  obtaining  the  quantities  in  the 
table.) 

WEDNESDAY,    FEBRUARY    5,    1892. 


Hour    

9  A.M 

IO 

II 

12  M. 

I   P  M 

2 

3 

4' 

Total  flow  per  hour  .  . 

35,217 

38,769 

32,892 

32,892 

34,049 

35,217 

36,490 

34  049 

5  P.M. 

6 

7 

8 

Q 

IO 

ii 

12 

Total  flow  per  hour  .  . 

32,892 

31,840 

31,840 

31,840 

29,301 

29,301 

29,301 

28,135 

THURSDAY,    FEBRUARY   6. 


I  A.M. 

28,135 

2      |         3 

28,135125,711 

4 

28.135 

26.833 

6     [       7 
26,833  29,461 

8 
31,840 

Total  flow  per  hour  ... 

Average  flow  per  hour,  31,213  gallons;  minimum  flow,  25,711  gallons;  max- 
imum flow,  38,769  gallons,  or  24$  increase  over  the  average. 

TABLE  No.  6. 

WATER-CONSUMPTION     AND     SEWAGE     FLOW,    ATLANTIC     CITY,    N.    J., 

DECEMBER,   I  SpI-NOVEMBER,   1892. 

(Average  Daily  Percentage  of  Excess  of  Water  Consumed  over  Sewage 
Pumped— by  Months.) 


<£  <£  |  December. 

rt 
3 
C 
M 

February. 

C 

ctf 
i 

t 

1 

i 

, 

3 
be 

3 

September. 

October. 

November. 

Exces 

53 
5  of  wa 

54 
iter-ta] 

61 

3s  ove 

64 
'  sewe 

36 

r-conn 

II 
actions 

36 

.  perce 

75 
mtage 

66 

18 
38 

The  average  daily  percentage  of  excess  for  the  year  =  45$. 
The  average  excess  of  water-taps  for  the  year  =  44$. 


4o 


SEWERAGE. 
TABLE  No.  7. 


RESULT  OF  A  GAUGING  BY  WEIR  MEASUREMENT  OF  THE  FLOW  OF 
THE  MAIN  OUTFALL  SEWER  OF  THE  STATE  INSANE  HOSPITAL 
AT  WESTON,  W.  VA.,  IN  JANUARY,  1891. 

(Made  by  GEO.  W.  RAFTER.  Condensed  from  "Sewage  Disposal  in  the 
United  States."  Self-closing  fixtures  were  used  in  the  building.  10,000  gallons 
per  day,  or  7  gallons  per  minute,  of  water  of  condensation  from  the  steam- 
heating  apparatus  was  discharged  into  the  sewer.) 


Day. 

Hour. 

Rate  in 
Gallons 
per  Min. 

Day. 

Hour. 

Rate  in 
Gallons 
per  Min. 

Day. 

Hour. 

Rate  in 
Gallons  i 
per  Min. 

Day. 

Hour. 

Rate  in 

Gallons 
perMin 

12 

78.75 

I  A.M. 

44-55 

I  P.M. 

99-45 

IA.M. 

34  65 

I  P.M. 

93-60 

2 

44-55 

2 

86.40 

2 

34.65 

2 

93.60 

3 

44-55 

3 

93.60 

3 

39-6o 

3 

75.60 

4 

44-55 

4 

75-6o 

4 

49-05 

. 

4 

75.60 

>> 

5 

49-  °5 

fi, 

5 

93-60 

5 

49-05 

^s 
rt 

5 

7O.2O 

rt 

6 

64.80 

rt 

6 

81.00 

6 

58.50 

"O 

V) 

6 

75.60 

1 

7 

75.60 

Cfl 

7 

93-00 

£ 

7 

70.20 

1) 

c 

7 

75  60 

3 

c« 

8 

86.40 

D 
jc* 

8 

58.50 

."2 

8 

86.40 

T3 
<U 

8 

70.20 

9 

105.30 

H 

9 

53-55 

M 

fe 

9 

105.30 

£ 

9 

58.50 

10 

117.90 

10 

53-55 

10 

86.40 

10 

53-55 

ii 

93.60 

ii 

44-55 

ii 

86.40 

n 

44-55 

12 

93-6o 

12 

44-55 

12 

105.30 

12 

44-55 

The  flow  of  the  Compton  Avenue  sewer,  St.  Louis,  Mo., 
was  gauged  hourly  from  March  15  to  23,  1880.  The  mini- 
mum flow  measured  was  88  gallons  per  minute,  the  maximum 
203  gallons,  and  the  mean  132  gallons. 

A  gauging  of  the  College  Street  sewer,  Burlington,  Vt., 
taken  at  15-minute  intervals  from  7.30  A.M.  to  10.30  P.M. 
gave  two  maximums,  one  at  7.45  A.M.,  the  other  at  9  A.M. ; 
these  were  each  140  gallons  per  minute.  The  minimum  flow 
was  65  gallons,  the  mean  115  gallons.  Fifty-four  houses 
were  connected;  the  tributary  population  was  325. 

Gaugings  made  at  Memphis,  Tenn.,  for  one  day  gave  a 
maximum  of  80  gallons  and  a  minimum  of  35  gallons  per 
minute. 

Gaugings  made  at  Kalamazoo,  Mich.,  in  1885,  from 
I  A.M  to  12  midnight  on  Monday,  March  9,  gave  a  minimum 


AMOUNT  OF  SEWAGE. 
Plate  No.  I. 


3,000,000 
2,000,000 
1,000,000 


4,000,000 
3,000,000 
2,000,000 
1,000,000 


4,000,000 
3,000,000 
2,000,000 
1,000,000 


5,000,000 
4,000,000 
3,000,000 
2,000,000 
1,000,000 


5,000,000 
4,000,000 
3,000,000 
2,000,000 
1,000,000 


12  6 

A.M. 


P.M 


EAST  SIDE  SEWER 

WEST    '•  •• 

BOTH  SEWERS  COMBINED 
•WATER  CONSUMPTION 


42  SEWERAGE. 

flow  of  224  gallons  per  minute,  a  maximum  of  287  gallons, 
and  a  mean  of  254  gallons. 

Gaugings  were  made  at  Des  Moines,  Iowa,  from  June  30 
to  July  16,  1895,  by  J.  A.  Moore  and  W.  J.  Thomas,  class 
of  '95,  Iowa  Agricultural  College  (see  Plate  I).  The  sewerage 
system  at  the  outlet  of  which  the  gaugings  were  taken  com- 
prised: on  the  west  side  235,000  feet  of  sewers,  contribu- 
tary  population  19,400,  15  hydraulic  elevators;  on  the  east 
side  29,000  feet  of  sewers,  contributary  population  8100,  3 
hydraulic  elevators. 

These  were  combined  sewers.  Rain  fell  on  two  Sundays 
only,  and  is  indicated  by  the  unusual  height  of  the  curve. 
Water-meters  were  used  on  the  services;  water  was  supplied 
to  33,700  persons,  but  the  amount  consumed  by  each  was 
not  ascertained,  the  average  consumption  for  the  city  being 
taken.  The  diagram  for  the  west  side  shows  noon-hour  stops 
of  factories.  The  high-water  curves  for  July  10,  n,  12,  and 
13  were  caused  by  the  water  company  flushing  dead-ends 
outside  of  the  limits  of  the  sewers  gauged.  On  the  I2th  the 
large  flow  in  the  west-side  sewer  was  probably  caused  by  a 
part  of  this  flushing-water  reaching  it. 

The  maximum  dry-weather  rate  of  flow  on  the  west  side 
was  at  10.15  A.M.  Friday,  July  12 — 175.3  gallons  per  capita. 

The  maximum  dry-weather  rate  of  flow  on  the  east  side 
was  at  6.30  P.M.  Tuesday,  July  2 — 142  gallons  per  capita. 

The  minimum  dry-weather  rate  of  flow  on  the  west  side 
occurred  at  4  A.M.  Saturday,  July  6 — 23.2  gallons  per  capita. 

The  minimum  dry-weather  rate  of  flow  on  the  east  side 
occurred  at  4.30  A.M.  Friday  July  5 — 22.5  gallons  per  capita. 

The  average  dry-weather  rate  of  flow  on  the  west  side  was 
66  gallons  per  capita. 

The  average  dry-weather  rate  of  flow  on  the  east  side  was 
74  gallons  per  capita. 

Table  No.  8  gives  the  water  pumped  and  the  sewage  dis- 


AMOUNT   OF  SEWAGE. 


43 


TABLE  No.  8. 


Date. 

Water. 

Sewage. 

81.656  of  the 
Water  Pumped. 

Remarks. 

July  3 

2,72O,OOO 

2,2OO,OOO 

2,219,520 

4 

1,829  oo° 

1,330,000 

,492,464 

Holiday 

5 

2,352,635 

2,O5O,OOO 

,919,7S<> 

6 

2,750,205 

2,040,000 

,244,167 

7 

1,809,110 

1,115,000 

,476,234 

Sunday;  rain 

8 

2,379,820 

2,030,000 

,941,933 

9 

2,437,825 

2,O2O,OOO 

,989,265 

charged  during  the  seven  days  when  the  measurements  taken 
were  apparently  reliable.  The  first  column  gives  the  total 
amount  of  water  pumped:  the  second,  the  total  sewage  flow; 
the  third,  8i.6#  of  the  first  column,  that  being  the  proportion 
between  the  number  of  water-taps  and  that  of  the  sewer-con- 
nections. The  close  correspondence  between  the  two  last 
columns  shows  what  an  excellent  index  the  water-consump- 
tion furnishes,  in  this  town  at  least,  of  the  total  house-sewage 
to  be  expected.  July  12  was  the  only  date  when  the  maxi- 
mum flow  of  the  west  side  exceeded  125  gallons  per  capita, 
and  then  for  two  hours  only.  The  average  for  this  side  was 
66  gallons.  Disregarding  the  maximum  of  the  I2th  instant, 
which  was  due  to  hydrant-flushing,  we  have  a  maximum  for 
this  side  89$  greater  than  the  average;  and  for  the  east  side 
the  maximum  was  92$  above  the  average.  The  record, 
however,  covers  two  holidays  out  of  the  seven,  making  the 
average  unusually  low;  also  the  general  average  for  that  time 
of  year  would  ordinarily  be  lower  than  that  for  an  entire  year. 
It  is  thought  that  these  include  all  the  published  records 
of  gaugings  of  sewage  flow  which  have  been  made  in  this 
country.  They  seem  to  point  uniformly  to  the  conclusions 
already  stated — that  the  winter  flow  of  sewage  is  greater  than 
the  summer;  that  the  maximum  and  minimum  flow  do  not 
ordinarily  vary  from  the  yearly  average  more  than  75$,  but 
frequently  do  by  50$;  that  the  house-sewage  per  capita  very 
nearly  equals  the  water-consumption  where  the  taps  and  sewer- 
connections  are  equal  in  number. 


44  SEWERAGE. 

The  engineer  must  select  and  use  with  a  great  deal  of 
judgment  all  the  data  obtainable  in  fixing  upon  the  quantities 
which  the  sewer  should  be  designed  to  carry.  The  method 
of  making  the  calculations  will  be  explained  more  at  length 
in  Chapter  VII. 


ART.  16.     AMOUNT  or  STORM-WATER. 


The  amount  of  storm-water  reaching  a  given  sewer 
depends  upon  the  rate  of  rainfall,  the  time  during  which  this 
rate  is  continued,  the  proportion  of  the  rainfall  which  flows 
off,  and  the  time  taken  by  a  raindrop  after  falling  to  reach 
the  point  under  consideration.  This  last  depends  upon  the 
shape,  extent,  and  nature  of  the  surface  over  which,  and  the 
length  and  grade  of  the  sewer  through  which,  it  must  flow. 

ART.  IT.     RATES  OF  RAINFALL. 

It  is  apparent  that  the  rate  at  which  the  water  reaches  the 
sewer  depends  to  a  greater  or  less  degree  on  the  rates  of  rain- 
fall from  minute  to  minute,  and  not  upon  the  amount  falling 
in  a  day  or  even  in  an  hour.  Records  giving  rainfalls  for 
these  latter  units  of  time  are,  therefore,  valueless  to  the 
sewerage  engineer.  It  is  only  within  recent  years  that  gauges 
have  been  used  which  automatically  register  the  rate  of  rain- 
fall at  each  moment  of  a  storm.  But  so  great  a  necessity  for 
such  records  has  been  felt  that  the  use  of  self-registering  rain- 
gauges  is  becoming  more  and  more  general,  and  in  most  of 
the  large  cities  continuous  record  of  the  rates  of  rainfall  is 
obtained  either  by  a  city  department  or  by  the  United  States 
Weather  Bureau. 

Since  the  maximum  amount  of  water  to  be  removed 
-determines  the  size  of  the  sewer,  we  are  concerned  only  with 
the  maximum  rates  or  those  near  the  maximum.  Rates  of 
heavy  rainfalls  for  various  cities  of  the  United  States  are 


AMOUNT   OF  SEWAGE.  45 

given  in  Table  No.  9.  Where  possible  several  high  rates 
during  the  same  or  consecutive  years  are  given  for  each 
locality,  but  no  attempt  has  been  made  to  give  a  record  of 
all  severe  storms  for  any  one  place  or  year.  An  examination 
of  rainfall  data  covering  many  years  shows  that  in  New 
England  a  rate  of  3.6  inches  an  hour  continuing  for  5  minutes 
may  be  expected  every  year  or  two,  a  rate  of  2  inches  con- 
tinuing for  20  minutes,  a  1. 5-inch  rate  continuing  for  30 
minutes,  and  I  inch  in  60  minutes.  In  New  York  State 
the  rate  may  be  about  20$  and  in  Pennsylvania  about  30^ 
higher.  In  Baltimore  and  Washington  we  may  expect  a 
5-inch  rate  for  5  minutes,  a  4-inch  rate  for  10  minutes,  a 
2.7-inch  rate  for  20  minutes,  a  2-inch  rate  for  30  minutes, 
and  1.4  inches  in  60  minutes.  In  New  Orleans  a  5.5-inch 
rate  for  5  minutes,  a  4.5-inch  rate  for  10  minutes,  a  3-inch 
rate  for  20  minutes,  a  2.5-inch  rate  for  30  minutes,  a  2-inch 
rate  for  60  minutes  or  even  more  may  be  expected.  In  the 
central  States  a  rate  of  3.7  inches  for  10  minutes,  2.8  inches 
for  20  minutes,  2.3  inches  for  30  minutes,  and  1.7  inches  in 
60  minutes  may  be  expected.  Further  data,  however,  may 
require  a  change  in  any  of  these  values. 

The  last  rates  in  the  table  are  given  to  show  what  down- 
pours sometimes  occur  in  certain  sections.  In  2  hours 
there  fell  at  St.  Kitts  more  than  12  inches;  how  much  more 
could  not  be  ascertained.  The  Palmetto  gauge  was  swept 
away  after  registering  12  inches  in  2  hours. 

The  records  seem  to  show,  where  any  information  on  the 
subject  is  given,  that  the  maximum  intensity  usually  lasts 
but  a  few  minutes,  seldom  more  than  ten;  that  it  sometimes 
occurs  at  the  beginning  of  a  storm,  but  in  a  great  majority  of 
instances  occurs  at  the  middle  or  end  of  it,  quite  a  number 
stopping  10  to  20  minutes  after  the  maximum  rate  is 
attained.  As  to  the  area  simultaneously  covered  by  the 
maximum  rates  of  fall,  almost  no  data  are  available. 


46 


S£  WERA  GE. 


TABLE  No.   9. 

MAXIMUM    AMOUNTS   OF   RAIN    FALLING    DURING  DIFFERENT  PERIODS 

OF    TIME. 


Length  of  Period  in  Minutes. 

Place  and  Date. 

5 

TO 

15 

20 

25 

3° 

45 

60 

Over  60. 

Amt. 

Dura- 
tion. 

0.50 

5.20 

24  h. 

Boston,  Oct.  12,  1895 
»         j-  1879-1891 

"        July  18,  1884 
Providence,  R.  I.,  May  18,  1877 
Aug.  29,  1877 
6,  1878 
"      28,  1882 
Ithaca,  N.  Y.,  Aug.  4,  1892.    Preceded  by 
5  hours  of  light  rain 
Mt.  Carmel,  N.  Y.,  July  2,  1897 
Morrisania,  Oct.  30,  1866 
New  York  City,  Sept.  19,  1894 
Aug.  19,  1893 
7  times  during  1869-1891 

3  ;;       ||      |;    ;; 

May  4,  1893 
1882             [sewer) 
July  6,    1896.    (Gorged   a 
Brooklyn,  N.  Y. 
Spring  Mount,  Pa.,  June  6,  1893 
'•    during  1893  (4  storms) 
Philadelphia,  Pa.,  2  times  during  1884-1891 

0.80 

2.56 

..... 

5-03 

!:3 

rib. 

i*h. 
2  h. 

o-35 

1  .20 

0.80 

o   fV. 

1.30 

3.60 
6.i7 

24  h. 
24  h. 

o  80 

I.OO 

2    60 

I  .00 

0.25'!.  oo 

....|l.OO 

i.  "78 

1.50 
T.rVi 



o.Kc 
o  60 

1.3° 

«        !!   3   '!      !! 

"              "      March,  1890 
Baltimore,  1896 

Washington,  D.C.,  2  times  during  1871-1891 

"       5     "             "          "       " 

o  06 

0.21 
0.25 

0.80 

°-35 
0.60 

i.  60 
0.80 
o  60 

0.46 
0.85 

0.58 
0.92 

0.6* 

0.95 

0.64 

0.83 

o-95 





1.3° 

.... 

1.50 





0.52 
O.SO 
0.40 
O.4O 
0.00 
0.25 

0-35 

0.14 
0.30 
0.07 

O.IO 

0.30 

0.85 
0.70 
°-75 

1.20 

0.60 

o-75 

1.20 
I  .OO 
1.20 
1.50 
I.OO 

i.  '48 
1.32 

1-75 
1.17 

1.78 
j'.'e'i 

T-95 

2.00 

1.25 

2.05 

1.87 

2-15 

2.  IO 

2.00 
2.70 
2.62 
2.45 
2.20 

3-40 
3-i9 
2.70 
2.32 

"                "     mean  of  many  rains 
New  Orleans,  June  17,  1895 
Aug.  13,  1894 
July  4, 

'  T4i 
Sept.,  1889  (2  storms) 
April  24,  1894.   Preceded   by 
6  hours  of  light  rain 

(Jacksonville,  Fla.,  U.  S.  Weather  Bureau, 
(•     1896 

1  Galveston,  Texas,  1896.      U.  S.  Weather 
f      Bureau 
Chicago,  once  during  1889-1891 
2  times    " 

Ohio  Valley,  July  16,  1896 
St.  Louis,  May  14,  1891 
Cleveland,  Ohio,  1896  1 

Detroit,  Mich.,        "     !U.  S.  Weather 
i      Bureau 
Little  Rock,  Ark.,  " 

San  Diego,  Cal.,  December,  1896 
Dampo,  Cal.,  August,  1891 
3almetto,  Nev.,     "       1890 

>  Island  of  St.  Kitts 

6.00 
3-3° 

2-35 

2  h. 
2  h. 

'ijh. 

•?  60 

0.65 

0.20 

0.61 

0.26 
0.30 

o-45 

0.90 

0.47 
0.70 

0.44 

o-37 
°-57 

»-*5 

0.85 
0.92 
0.77 
0.47 
0.65 

1.40 

0.90 
1.30 
0.82 
0.62 
0.77 

i-55 

I    01 

!-57 
0.91 

°-75 
0.90 

I.78 

I.7I 

I-I5 
1.50 

0.88 
i  .10 

i.  88 

1.99 

i.  80 

I.OO 

1.23 



:.::: 

•  '•'•' 

:;:;: 

o   Sri 

o  60 

.  10 

I-75 
3-3^ 

2h. 
2h. 

0.28 
0.04 

0.15 
0.38 
0.25 

0.06 
0'35 

0.58 
O.I9 

°-45 
o-57 
0.50 
o-33 

0.88 
0.49 

£g 

o-75 
0.46 

l-*3 
0.79 

I.OO 

0.91 
0-95 
0.60 

1.23 
1.04 
1.07 
1.13 
0.99 

0.66 

1.38 

i-3i 
1.14 
1.30 
i  .02 
0.70 

i-73 







1.70 
0.79 

1.78 

0.91 
o  82 

::.":; 



... 

.... 

"•5+ 
8  8 



36  j- 

12    + 

24  h. 

2  h. 

AMOUNT  OF  SEWAGE.  47 

ART.  18.     RUN-OFF  DATA. 

The  data  concerning  rates  of  run-off  as  compared  with 
rainfall  during  the  same  time  are  very  meagre.  The  total 
annual  or  monthly  proportion  of  run-off  has  been  ascertained 
in  many  different  localities,  but  even  this  is  for  natural 
wooded  surfaces  or  fields  only.  The  number  of  careful  gaug- 
ings  in  this  country  of  rainfall  within  city  limits  and  of  con- 
temporaneous sewer  discharge  from  a  known  area  probably 
does  not  exceed  a  half  dozen. 

One  of  the  most  recent,  extensive,  and  scientific  of  such 
gaugings  was  that  made  at  New  Orleans  in  1894-5  under  the 
direction  of  the  Engineering  Committee  on  Drainage.  Un- 
fortunately for  its  general  usefulness  in  the  study  of  run-off 
problems  the  run-off  measured  probably  included  seepage 
from  a  soil  lower  than,  and  consequently  more  or  less  saturated 
by,  the  Mississippi  River.  The  rainfall  was  recorded  contin- 
uously at  several  points  throughout  the  city,  and  several  of 
the  maximum  rates  are  given  in  Table  No.  9.  A  continuous 
record  was  also  kept  of  the  amount  of  water  reaching  the 
drainage-ditches  from  above  and  beneath  the  surface  of  the 
soil.  From  data  thus  and  otherwise  obtained  the  committee 
prepared  curve-diagrams  (Plate  No.  II)  for  the  calculation  of 
run-off  from  areas  of  different  extent,  character,  and  grade  of 
surface  in  New  Orleans.  "  The  set  marked  A  represents  the 
run-off  from  densely  built-up  parts;  the  set  marked  B  applies 
to  the  areas  having  small  yards,  or  a  medium  density  of 
population;  the  set  marked  C  applies  to  the  sparsely  built-up 
parts,  or  those  having  large  yards;  and  the  set  marked  D 
applies  to  the  rural  areas.  These  curves,  therefore,  indicate 
the  maximum  rate  of  rainfall  which  it  is  proposed  to  provide 
for,  and  which  is  assumed  to  reach  the  drains  and  canals  from 
the  respective  areas. 

"  They  do  not  warrant  the  assumption,  however,  that  the 


4$  SEWEKAGE. 

discharge  will  never  exceed  the  quantities  given  for  it;  in  fact 
it  is  certain  that  they  will  be  exceeded,  but  at  such  rare  and 
indefinite  intervals  that  their  consideration  is  not  justified.  It 
should  also  be  remarked  that  the  curves  are  based  upon  the 
assumption  that  .  .  .  the  water  enters  the  drains  promptly, 
as  is  the  case  in  most  other  cities."  (Report  of  the  Engineer- 
ing Committee — B.  M.  Harrod,  Henry  B.  Richardson,  and 
Rudolph  Hering — on  the  Drainage  of  the  City  of  New 
Orleans;  1895.) 

A  number  of  gaugings  have  been  made  in  Washington,, 
D.  C.,  in  districts  whose  streets  are  almost  entirely  paved 
with  asphalt.  In  one  case  "  the  flow  in  the  sewer  rose 
almost  immediately  after  the  rain  began  and  fell  to  its  normal 
level  within  a  few  minutes  after  the  rain  ceased."  During 
another  storm  "  at  its  maximum  period  the  rain  fell  for  37 
minutes  at  the  rate  of  0.9  of  an  inch  per  hour.  The  sewer- 
gauge  rose  to  a  height  of  3.7  feet,  giving  about  0.47  of  the 
capacity  of  the  sewer  and  indicating  no  loss  whatever  by 
absorption  or  evaporation  during  the  time  of  maximum  flow." 
(Hoxie  on  "  Excessive  Rainfalls,"  Transactions  Am.  Soc. 
C.  E.,  vol.  xxv.)  This  sewer  received  the  drainage  of  200 
acres. 

Gaugings  made  in  Rochester  by  Emil  Kuichling  are  too 
extensive  to  be  quoted  here,  but  the  tables  may  be  found  in 
the  Transactions  Am.  Soc.  C.  E.,  vol.  XX,  pages  1-60, 
accompanied  by  an  excellent  discussion  on  the  subject  of  run- 
off. The  conclusions  drawn  from  these  by  the  author  of  that 
paper  are  quoted,  as  stating  clearly  the  general  principles  on 
which  are  founded  the  rational  methods  of  calculating  run-off. 
The  gaugings,  he  says,  "  point  unmistakably  to  the  following 
general  conclusions: 

"  I.  The  percentage  of  the  rainfall  discharged  from  any 
given  drainage-area  is  nearly  constant  for  rains  of  all  consider- 
able intensity  and  lasting  equal  periods  of  time.  This  cir- 


AMOUNT  OF  SEWAGE. 


OF   THK 

UNIVERSITY 
"2iCALIFO*J§> 


MAXIMUM  FLOW  FROM  DRAINAGE  AREA  IN  CUBIC  FEET  PER  SECOND 


50  SEWERAGE. 

cumstance  can  be  attributed  only  to  the  fact  that  the  amount 
of  impervious  surface  on  a  definite  drainage-area  is  also 
practically  constant  during  the  time  occupied  by  the  experi- 
ments. 

"2.  The  said  percentage  varies  directly  with  the  degree 
of  urban  development  of  the  district,  or,  in  other  words,  with 
the  amount  of  impervious  surface  thereon.  .  .  . 

''3.  The  said  percentage  increases  rapidly,  and  directly 
or  uniformly  with  the  duration  of  the  maximum  intensity  of 
the  rainfall,  until  a  period  is  reached  which  is  equal  to  the 
time  required  for  the  concentration  of  the  drainage-waters 
from  the  entire  tributary  area  at  the  point  of  observation ; 
but  if  the  rainfall  continues  at  the  same  intensity  for  a  long1 
period,  the  said  percentage  will  continue  to  increase  for  the 
additional  interval  of  time  at  a  much  smaller  rate  than  pre- 
viously. This  circumstance  is  manifestly  attributable  to  the 
fact  that  the  permeable  surface  is  gradually  becoming  satu- 
rated and  is  beginning  to  shed  some  of  the  water  falling  upon 
it;  or,  in  other  words,  the  proportion  of  impervious  surface 
slowly  increases  with  the  duration  of  the  rainfall. 

"  4.  The  said  percentage  becomes  larger  when  a  moderate 
rain  has  immediately  preceded  a  heavy  shower,  thereby  par- 
tially saturating  the  permeable  territory  and  correspondingly 
increasing  the  extent  of  impervious  surface. 

"5.  The  sewer  discharge  varies  promptly  with  all  appre- 
ciable fluctuations  in  the  intensity  of  the  rainfall  and  thus 
constitutes  an  exceedingly  sensitive  index  of  the  rain  and  its 
variations  of  intensity. 

"  6.  The  diagrams  also  show  that  the  time  when  the  rate 
of  increase  in  the  said  percentage  of  discharge  changes 
abruptly  from  a  high  to  a  low  figure  agrees  closely  with  the 
computed  lengths  of  time  required  for  the  concentration  of  the 
storm-waters  from  the  whole  tributary  area,  and  hence  the 
said  percentages  at  such  times  may  be  taken  as  the  proportion 


AMOUNT   OF  SEWAGE.  51 

of  impervious  surface  upon  the  respective  areas."  (Transac- 
tions Am.  Soc.  C.  E.,  vol.  XX,  page  37.) 

"  The  Nagpoor  (India)  storage  reservoir  receives  the 
flow  from  a  watershed  of  6.6  square  miles.  With  a  very 
absorbent  natural  surface  that  watershed  has  nevertheless 
delivered  to  the  reservoir  in  170  minutes  98$  of  a  downpour 
upon  its  entire  area  of  2.2  inches  in  80  minutes,  when  the 
power  of  absorption  of  the  soil  had  been  satisfied."  (Hoxie). 

Many  instances  could  be  named  where  storm-sewers  which 
were  designed  to  carry  a  run-off  of  one  cubic  foot  per  second 
have  caused  serious  damage  by  their  too  small  capacity; 
several  where  even  a  capacity  of  two  cubic  feet  per  second 
was  insufficient.  (One  inch  of  rainfall  per  hour  equals  one 
cubic  foot  per  second  per  acre  almost  exactly.)  Not  many 
years  ago  a  sewer  was  considered  by  most  engineers  to  be  of 
ample  size  if  it  was  designed  for  a  rainfall  of  one  inch  per 
hour,  one  half  running  off;  but  the  insufficiency  o'f  this  rule 
has  been  learned  by  costly  experience. 

Accounts  of  accidents  through  insufficient  sewer  dimen- 
sions are  unfortunately  more  numerous  than  data  giving  exact 
figures  of  unusual  volumes  of  rainfall  reaching  sewers. 

An  analysis  of  the  available  data  seems  to  point  to  the 
following  conclusions: 

That  the  total  run-off  from  any  area  is  directly  propor- 
tional to  the  imperviousness  of  the  surface,  and  that  this 
imperviousness  increases  with  the  length  of  the  storm,  unless 
it  is  already  ioo#. 

That  very  nearly  100$  of  the  water  falling  upon  an  im- 
pervious surface  flows  immediately  to  the  sewer  unless  held 
back  by  obstructions  in  the  street,  roof-gutters,  or  sewer- 
inlets — the  last  including  insufficiency  of  size  of  the  inlet.  A 
small  percentage,  however,  is  usually  evaporated  at  once. 

That  the  proportion  of  the  rainfall  on  any  given  imper- 
vious area  which  reaches  any  particular  point  in  the  sewer 


52  SEWERAGE. 

system  increases  with  the  length  of  the  storm  up  to  the 
time  when  the  run-off  from  the  most  distant  part  of  said  area 
reaches  the  point  of  observation;  after  which  the  run- off  very 
nearly  equals  the  rainfall  upon  said  area  while  the  rate  of  fall 
remains  constant. 

That  the  percentage  of  imperviousness  of  the  surface  may 
vary  from  ofo  to  100$,  being  the  first  in  the  case  of  very 
porous  soil  under  natural  conditions  at  the  beginning  of  a  rain, 
and  the  last  in  an  urban  district  where  streets,  sidewalks,  and 
yards  are  all  paved,  or  occasionally  where  a  dense  clay  soil  is 
saturated  by  previous  rainfall. 


ART.  19.  FORMULAS  FOR  STORM-  WATER  RUN-OFF.. 

Many  attempts  have  been  made  to  construct  a  simple 
general  formula  for  obtaining  the  run-off  from  any  area.  The 
best  known  of  these  are  as  follows  : 


Craig  :  D  =  ^oBN  hyp.  log  ~g-  . 

D  =  discharge  in  cubic  feet  per  second  ; 
L  =  extreme  length  of  drainage-area  ; 
B  =.  mean  breadth  of  drainage-area  ; 
N  '=  constant  varying  from  0.37  to  1.95. 

M 

Dredge:  Q=  1300^. 

L  =  length  of  watershed  ; 

M  =  area  in  square  miles. 
Dickens:  D  =  825^*. 

D  =  discharge  in  cubic  feet  per  second  ; 

M  =  drainage-area  in  square  miles. 
Fanning:  Q  =  2OoM*. 

Q  =  discharge  in  cubic  feet  per  second  ; 

M  =  drainage-area  in  square  miles. 


AMOUNT   OF  SEWAGE. 


53 


Burkli-Ziegler:   Q  = 


-r. 


c  =  constant — 0.75  for  paved  streets,  0.31  for 

macadamized  streets; 
R  =  average  rate  during  heaviest  fall  in  cubic 

feet  per  second  per  acre ; 
5  =  general  fall  of  area  per  lOOO; 
Q  =  cubic  feet  per  second  per  acre  reaching 

sewers ; 
A  =  drainage-area  in  acres. 


D 

D  =  diameter  of  sewer  in  feet* 
6"  =  sine  of  inclination ; 
N  =  number  of  acres  in  area. 
Maximum  rainfall  of  one  inch,  one  half  running  off. 


Hawksley:  log  D  = 


3   log  A  +  log  N  +  6.8 


D  =  diameter  of  sewer  in  inches ; 

A  =  number  of  acres  to  be  drained; 

N  —  length  in  feet  in  which  sewer  falls  one 

foot. 
City  or  suburban  surfaces. 

2  log  A  +  log  N  —  3.79 
Adams :        log  D  =  —  ^ . 

A  =  area  in  acres ; 
TV—  as  in  Hawksley; 
D  =  diameter  in  feet. 

For  one  inch  rainfall,  one  half  running  off. 


McMath:  Q  = 


Terms  as  in  Burkli-Ziegler;  R  taken  at  St. 
Louis  as  2.75  inches. 


54  SEWERAGE. 

Kuichling:  Q  =  Aat(b  —  ct}. 

Q  =  discharge  in  cubic  feet  per  second ; 
A  =  drainage-area  in  acres ; 
t  =  duration    in    minutes    of    the    intensity 

b  =  2.1         i  for  Rochester,  N.  Y.      (Kuich- 
c  =  0.0205  ;       lmg  recently  gives  as  a  for- 
mula representing  storms  of 
the  second  class  at  Rochester : 

r  =  — g,  in  which  r  =  rate  in 

inches  per  hour.) 
proportion  of  impervious  surface 


The  following,  known  as  Roe's  tables,  gives  the  number 
of  acres  of  urban  surfaces  which  can  be  drained  by  sewers  of 
different  diameters  and  at  different  grades.  It  is  no  longer 
in  general  use. 


Inclination,  Fall,  or  Slope 


Inner  Diameter  or  Bore  of  Sewer  in  Feet. 


of  Sewer. 

2 

39 
43 
50 
63 
7S 
90 
H5 

2* 

3 

4 

277 
308 

355 
460 

59° 
670 

730 

5 

6 

7 

8 

9 

10 

Level. 
i  in.  in  10  ft.,  or  i:  480. 

67 

75 
87 
H3 
143 
165 
182 

120 
135 
155 
203 

257 
295 
318 

570 
630 

735 
950 

1200 

1385 
1500 

IO2O 
III7 
1318 
1692 
2180 
2486 
2675 

1725 
1925 
2225 

2875 
3700 
4225 
4550 

2850 
3025 
3500 
4500 

5825 
6625 
7125 

4125 

4425 
5100 

6575 
7850 

5825 
6250 

7175 
9250 
II,O5O 

1  "  "  "  "  "   :240.   . 

lif            .00... 

2  "   "  "  "  "   '60  .  .  .  . 

The  formulas  of  Craig,  Dredge,  Dickens,  and  Fanning 
apply  to  natural  surfaces  and  have  the  shape  and  extent  of 
the  drainage-area  as  the  only  variables.  The  Burkli-Ziegler, 
Kirkwood,  and  McMath  formulas  take  into  account  also  the 
slope  of  the  surface.  The  Burkli-Ziegler  and  Kuichling  allow 
for  varying  conditions  of  surface,  and,  together  with  the 
McMath,  for  varying  rates  of  rainfall.  All  these  formulas 
except  the  three  last  mentioned  are  based  on  an  assumed 
maximum  rate  of  rainfall. 


AMOUNT   OF  SEWAGE. 


55 


Roe's  tables  give  the  diameter  of  sewer  necessary  to  meet 
various  conditions  of  area  and  sewer  grade.  As  in  a  level 
sewer  the  surface  of  the  water  must  have  some  fall  if  there  is 
to  be  any  flow,  the  quantities  given  for  a  level  grade  can 
apply  only  to  a  limited  length  of  sewer.  None  of  these 
formulas  is  satisfactory  for  all  cases,  because  none  takes  into 
account  all  the  variable  conditions.  Those  which  are  prob- 
ably the  most  frequently  used  are  the  Burkli-Ziegler, 
McMath,  and  Kuichling,  and  these  are  seen  to  be  the  ones 
containing  the  most  variables.  The  proper  test  of  any 
formula  is  to  calculate  by  it  from  known  data  quantities 
which  are  also  known.  Many  such  tests  of  all  these  formulas 
have  been  made,  and  it  has  been  found  that  there  are  few,  if 
any,  cases  in  which  all  will  give  results  practically  identical  or 
equal  to  the  actual  quantities  as  measured.  Such  a  compari- 
son is  given  of  Roe's  tables,  Hawksley's,  Kirkwood's,  and 
Biirkli-Ziegler's  formulas,  and  the  actual  gaugings  of  a  sewer 
in  Washington  made  in  1884  (from  paper  by  Capt.  R.  L. 
Hoxie  read  before  the  Am.  Soc.  C.  E.  July  2,  1886): 


Rainfall. 

Roe's  Tables. 

Hawksley. 

Kirkwood. 

Biirkli- 
Ziegler. 

Actual 
Maximum 
Flow. 

0.5"  in  15  min.  .  .  . 
0.55"  in  37  min.. 

36.3 
36  3 

43-2 
43-2 

51.7 
51-7 

137-6 
6l.g 

300 
1  80 

The  discrepancies  are  largely  due  to  the  causes  already 
referred  to — that  factors  are  taken  as  constants  which  are 
really  variables,  and  hence  each  formula  can  give  correct 
results  for  certain  cases  only.  In  most  the  constant  is  sup- 
posed to  be  derived  from  maximum  rates  of  rainfall,  but  such 
data  were  until  recently  incomplete  and  inaccurate.  Also, 
since  the  authors  of  the  older  formulas  were  Europeans  or 
derived  their  data  from  European  sources,  the  maximums 
were  those  for  Europe  and  are  not  applicable  to  this  country. 
Also  the  character  of  the  majority  of  city-street  surfaces  has 


5  6  SEWEXAGE. 

changed  since  that  time.  The  Kuichling,  Biirkli-Ziegler,  and 
McMath  formulas  recognize  the  variableness  in  drainage- 
surfaces. 

It  is  possible  that  a  formula  can  be  devised  which  shall 
represent  by  variable  factors  all  the  conditions  which  have 
been  shown  to  affect  the  run-off.  But  it  can  hardly  be 
expected  that  such  a  formula  can  be  other  than  cumbersome; 
and  it  is  probable  that  the  shortest  method  which  is  at  all 
rational  and  accurate  in  all  cases  is  that  of  subdividing  the 
calculation,  and  adapting  a  general  method  rather  than  a 
general  formula  to  the  peculiar  conditions  of  each  case. 
Such  a  method  is  recommended  and  will  be  outlined  further 
on. 

Many  engineers,  however,  use  some  one  of  the  formulas 
given,  and  a  large  majority  of  the  storm-sewers  built  in  this 
country  are  probably  so  designed — in  spite  of  the  fact  that 
McMath  considers  his  formula  (which  is  probably  the  most 
popular)  as  adapted  to  large  areas  only,  and  that  it  is  derived 
in  an  entirely  empirical  manner  from  St.  Louis  data  only;  and 
that  Kuichling  has  "  finally  abandoned  the  attempt  to  estab- 
lish a  general  formula  for  run-off,"  although  the  one  bearing 
his  name  is  largely  general  in  application  and  rational  in  origin 
and  construction. 

ART.  20.     EXPEDIENCY  OF  PROVIDING  FOR  EXCESSIVE 

STORMS. 

An  examination  of  rainfall  records  shows  no  apparent  law 
of  frequency  of  excessive  storms.  It  can  be  said  as  a  general 
statement,  however,  that  a  rate  of  fall  within  certain  limits 
may  be  expected  almost  any  month;  one  within  higher  limits 
five  or  more  times  in  ten  years  (these  are  the  storms  referred 
to  in  Art.  16);  and  a  phenomenal  downpour  at  most  irregular 
intervals,  usually  many  years  apart.  Should  the  sewer  be 
designed  to  carry  the  run-off  from  storms  of  the  first  class 


AMOUNT  OF  SEWAGE.  57 

only,  of  the  second  class,  or  be  of  the  greatest  size  demanded 
by  the  third  class  ? 

That  the  last  is  desirable  will  not  be  disputed,  but  both 
practical  and  financial  difficulties  frequently  oppose  this 
course.  The  practical  ones,  however,  in  most,  if  not  all,  cases 
resolve  themselves  into  financial  ones;  and  the  question 
becomes  one  of  dollars  and  cents,  and  to  a  certain  extent  also 
of  public  convenience,  which  cannot  be  assigned  a  money 
value.  To  accommodate  the  second  class  of  storms  may 
require  a  sewer  of  three  or  four  times  the  capacity  of  one 
which  would  suffice  for  the  run-off  from  the  first  class,  and 
the  third  class  a  capacity  two  or  three  times  that  of  the 
second.  The  result  of  providing  capacity  for  the  first  class 
only  would  probably  be  flooding  of  streets  and  cellars  one  or 
more  times  almost  every  year;  for  the  second  class,  flooding 
at  intervals  of  several  years;  for  the  third  class,  perfect 
immunity  from  floods. 

The  loss  resulting  from  a  flooding  of  streets  and  cellars  by 
water  more  or  less  foul  may  be  very  considerable;  goods  may 
be  damaged,  business  suspended,  foundations  weakened, 
health  threatened  by  the  dampness  lingering  after  the  floods 
have  withdrawn ;  also  real-estate  values  in  a  district  liable  to 
floods  will  depreciate  and  the  city  as  a  whole  will  be  a  loser 
by  increased  tax  rates  to  meet  the  decreased  valuation.  On 
the  other  hand  as  the  capacity  of  a  sewer  increases  so  does 
the  cost,  and  this  fact  may  place  an  urgent,  even  an  impera- 
tive, limit  to  either  the  capacity  or  the  extent  of  the  sewers  to 
be  built.  The  relative  cost  of  sewers  of  different  capacities 
(other  things  supposedly  equal)  in  Washington,  D.  C.,  for 
about  10  years  is  given  in  the  following  table  (adapted  from 
one  prepared  by  Capt.  Hoxie).  The  unit  of  capacity  is  that 
of  a  12-inch  pipe. 

The  exact  proportion  between  the  capacity  and  the  cost, 
and  the  rule  of  their  relative  increase,  will  vary  with  different 


SEWERAGE. 
TABLE  No.  10. 


Number  of 

Relative 

Number  of 

Relative 

Number  of 

Relative 

Units  of 

Cost 

Units  of 

Cost 

Units  of 

Cost 

Capacity. 

per  Foot. 

Capacity. 

per  Foot. 

Capacity. 

per  Foot. 

I 

I  000 

6 

1.920 

20 

3.170 

2 

1.  174 

7 

2.090 

30 

3.480 

3 

1.388 

8 

2.250 

40 

4.030 

4 

I-S^? 

9 

2.410 

50 

4.170 

5 

1-743 

10 

2.570 

methods  of  construction,  depth  of  sewer,  etc. ;  and  in  many 
localities  the  cost  will  be  found  to  increase  more  rapidly 
relative  to  the  capacity  than  is  indicated  by  Table  No.  10. 
But  in  any  case  it  will  be  found  that  the  increase  of  cost  is 
much  less  rapid  than  that  of  capacity.  Using  the  table  of 
cost  of  Washington  sewers,  a  sewer  of  three  times  the  capacity 
of  a  12-inch  pipe  would  cost  1.388  units  of  value.  If  this 
would  just  suffice  for  the  heaviest  storms  of  the  first  class  on 
a  given  area  one  of  a  capacity  ample  for  the  maximum  of  the 
second  class,  or  four  times  as  great,  would  cost  2.8  units  of 
value,  or  about  twice  as  much;  and  one  capable  of  removing 
the  run-off  from  the  greatest  downpours,  or  twelve  times 
capacity  of  the  first,  would  cost  3.75  units  of  value,  or  only 
2.7  times  as  much  as  the  first.  Moreover,  as  we  shall  see 
later,  the  larger  mains  need  to  increase  less  rapidly  in  capacity, 
and  hence  in  cost,  to  accommodate  the  heavier  storms  than 
do  the  smaller  laterals  used  in  this  illustration. 

The  decision  as  to  which  class  of  storms  the  size  shall  be 
adapted  to  must  be  made  for  each  case  by  the  engineer  or 
the  city  authorities  as  their  judgment  dictates.  But  prob- 
ably in  nine  cases  out  of  ten  the  truest  economy  will  be 
observed  by  constructing  sewers  sufficient  for  the  second,  or 
even  in  some  cases  the  third,  class  of  storms.  The  damage 
likely  to  result  from  the  use  of  sewers  of  too  small  capacity, 
which  damage  is  to  be  balanced  against  the  extra  cost  of 
larger  ones,  will  depend  upon  circumstances.  '*  If  the  sur- 


AMOUNT   OF  SEWAGE.  ,        S9 

face  flow  upon  the  streets  passes  off  to  a  proper  outlet  with- 
out causing  damage  or  inconvenience  the  flood  is  well 
disposed  of.  If  not,  there  is  danger  in  permitting  storm- 
water  to  accumulate  upon  streets  with  steep  grades.  It 
becomes  a  torrent  flowing  with  great  velocity,  and  cannot 
then  be  captured  by  inlets  designed  to  arrest,  each,  its  share 
of  shallow  gutter  flow  with  small  velocity.  It  moves  rapidly 
down  to  valleys  or  basins  without  surface  outlet;  here  it 
floods  the  surface,  because  inlets  to  receive  it  as  fast  as  it 
comes  can  rarely  be  constructed — even  should  the  drains  here 
be  of  sufficient  capacity.  Inlets  for  large  volumes  of  water 
in  city  streets  are  apt  to  be  pitfalls  for  pedestrians  and  traps 
for  cart-wheels  and  horses'  feet.  If  the  drains  of  the  inun- 
dated district  are  of  insufficient  capacity  the  consquences  are, 
of  course,  disastrous."  (Hoxie,  "  Excessive  Rainfalls.") 

As  suggested  in  this  quotation,  it  is  possible  in  many 
localities  to  lead  the  surplus  water  of  severe  storms  over  the 
surface  to  the  nearest  natural  watercourse,  and  this  without 
any  damage  resulting,  although  it  may  be  temporarily  incon- 
venient. But  in  a  city  where  all  small  streams  have  been 
walled  in  or  diverted  to  sewers  this  is  possible  only  along  a 
water  front. 


CHAPTER   IV. 
FLOW    IN   SEWERS. 

ART.  21.     FUNDAMENTAL  THEORIES. 

THE  flow  in  an  ordinary  sewer  must  be  due  to  one  cause 
only — the  attraction  of  gravitation.  The  velocity  of  this  flow 
is  retarded  by  friction  and  other  obstacles  affecting  it  along 
the  line  of  the  sewer. 

The  general  formula  for  the  velocity  due  to  gravity  of  a 
freely  falling  body  is  V  =  Vzgh,  where  V  is  velocity  in  feet 
per  second,  h  is  head  in  feet,  and  g  is  acceleration  due  to 
gravity,  being  about  32.16  feet  per  second.  In  the  case  of 
running  water  h  is  the  fall  of  the  surface  of  the  water  from 
the  point  of  no  motion  to  the  point  in  question.  Therefore 
if  there  were  no  opposing  forces  a  stream  would  flow  more 
and  more  rapidly  along  its  course  as  the  total  head  became 
greater;  and  its  velocity  would  become  constant  only  when 
the  surface  was  level,  and  therefore  h  constant.  There  is, 
however,  friction  between  the  moving  water  and  the  sides  of 
a  sewer,  and  this  must  be  overcome  by  some  force.  Since 
the  only  force  available  is  that  due  to  gravity,  called  into  play 
by  the  creation  of  a  head  ^,  a  part  of  this  force  must  be  used 
in  overcoming  friction.  If  it  is  not  all  so  used  the  remainder 
goes  to  create  additional  velocity.  Friction,  it  is  found, 
increases  with  the  velocity  of  the  moving  body,  so  that,  as 
additional  increments  of  speed  are  created  by  ^,  a  larger  pro- 
portion of  the  head  is  consumed  in  overcoming  friction,  until 
at  last  all  of  h  is  so  consumed  and  none  goes  to  increasing  the 

60 


FLOW  IN  SEWEKS.  6  1 

velocity  —  that  is,  the  velocity  remains  constant.  Friction  also 
varies  with  the  roughness  of  the  surface.  The  total  amount 
of  energy  lost  in  friction  also  increases  with  the  duration  of  its 
action,  which  is  proportional  to  the  distance  travelled  /.  It 
is  found  that  at  least  one  other  condition  affects  the  amount 
of  friction  in  sewers,  viz.,  the  proportion  between  the  cross- 
sectional  area  of  the  stream  and  the  length  in  this  cross-section 
of  the  line  of  contact  between  the  water  and  the  bed  of  the 
stream  ;  the  greater  the  first  is  in  proportion  to  the  second  the 
less  the  effect  of  friction  upon  the  mass  as  a  whole.  This 

area  of  section 
proportion,  or  wetted  perimeter'  1S  customarily  represented 

by  R  and  is  called  "  hydraulic  radius  "  or  "  mean  depth." 

From  these  considerations  it  follows  that  V  varies  as  V2gh 
and  asf(R),  and  inversely  as/(/).  The  effect  of  roughness 
may  be  represented  by  a  factor  a.  A  formula  for  velocity 

would  therefore  be  in  the  form  V  '=  a  —  •     In   17S3 


Brahms  proposed  as  a  formula  representing  the  resultant  effect 
of  these  accelerating  and  retarding  influences  V  =  c  VRS,  in 
which  V  =  mean  velocity  of  current,  c  is  an  empirical  constant 
which  includes  V2g  and  a,  R  is  the  hydraulic  radius,  and  5  is 

the  sine  of  the  surface  slope,  or  j.     This  formula,  now  gen- 

erally called  Ch£zy's  formula,  has  been  made  the  basis  of 
others,  most  of  which  differ  among  themselves  only  in  the 
values  given  to  c\  but  it  is  now  recognized  that  V  does 
not  vary  exactly  as  the  square  root  of  R  and  of  5;  that  is, 


that  f(R)  and  /(/)  in  the  formula  V=  a  are   not 


exactly    VR   and    Vl\    but    they   approximate    it,   and    this 
formula  may  therefore  be  written 


<>2  SEWERAGE. 

/-// r>\ 

•b  f,f /x    being  equal  to  the  £  of  Chezy's  formula.      From  this 

it  follows  that  c  is  not  a  constant  for  any  particular  sewer  or 
stream,  but  varies  with  both  R  and  5.  The  principal  cause 
affecting  the  value  of  cy  however,  is  the  condition  as  to 
roughness  of  the  wetted  perimeter. 

If  we  wish  to  obtain  the  velocity  of  flow  in  any  sewer  by 
this  formula  it  is  necessary  to  select  proper  values  for  c,  R, 
and  5.  5  can  be  readily  obtained  by  dividing  h  by  /.  The 
value  of  c  and  R  and  their  relation  to  V  will  now  be  discussed. 

For  c  most  of  the  older  formulas  give  constant  values;  but 
since  V  varies  with  different  materials  of  channel-walls,  whose 
character  does  not  affect  the  values  of  R  and  S,  this  variation 
must  be  recognized  in  a  variable  c  by  means  of  a  new  factor 
or  by  a  new  equation.  Most  of  the  efforts  looking  to  greater 
accuracy  have  been  directed  toward  determining  values  for 
c  and  thousands  of  experiments  have  been  made  for  this 
purpose.  D'Arcy's  value,  somewhat  simplified  and  for  feet 
measure,  is 

_( 155256  y 

~  \\2D-\-   ll  ' 

Bazin's  value  for  cut  stone  and  brick-work  is 

I 


c  =. 


.0000133 


(4.354  +  ^ 


Eytelwein's  value  is  c  =  93.4. 

The  formula  evolved  from  the  records  of  a  large  number 
of  experiments  by  Messrs.  Ganguillet  and  Kutter,  usually 
called  "  Kutter's  formula,"  is  now  generally  held  to  give 
results  more  nearly  approximating  the  actual  velocities  than 
any  other.  This  formula  is,  for  English  measure, 

.00281        1.811 
4I.6+-- c— +  -; 


c  = 


FLO W  IN  SEWERS.  63 

in  which  n  is  a  "  coefficient  of  roughness  "  of  the  sides  of  the 
channel,  such  coefficient  having  been  obtained  by  averaging 
many  experiments.  In  the  selection  of  value  for  n  great  care 
and  judgment  must  be  exercised,  particularly  for  small 
sewers,  in  the  calculation  for  which  n  has  a  greater  effect  than 
in  that  for  large  channels. 

The  values  of  n  are  approximately : 

Sides  and  bottom  of  channel  lined  with  well-planed  timber.  .009 
With  neat  cement,  clean  glazed  sewer-pipe,  and  very 

smooth  iron  pipe . . . .  .010 

With  I  : 3  cement  mortar  or  smooth  iron  pipe on 

With  unplaned  timber  and  ordinary  iron  pipe 012 

With  smooth  brick-work  or  ordinary  pipe  sewers 013 

With  ordinary  brick-work   015 

With  rubble  or  granite-block  paving 017 

Kutter's  formula  is  seen  to  provide  for  variations  in  c  due 
not  only  to  the  character  of  the  channel  but  also  to  changes 
in  R  and  ,S. 

This  formula  has  been  used  to  calculate  the  tables  Nos. 
n  and  12,  n  being  taken  as  .013  in  the  former  and  .015  in 
the  latter.  If  it  is  desired  to  use  another  value  of  n  the 
corresponding  values  of  velocity  and  discharge  can  be  obtained 
very  approximately  by  multiplying  the  quantities  given  in 
each  table  by  the  factors  given  below  it  for  that  purpose. 
For  ordinary  pipe  or  good  brick  sewers  n  may  be  taken  as 
,013,  for  ordinary  brick  or  smooth  stone  as  .015.  For  extra 
smooth  work  n  may  be  taken  as  .oil. 

The  uncertainties  necessarily  existing  in  the  estimates  of 
the  amount  of  sewage  to  be  provided  for  and  the  difficulty  of 
selecting  just  the  proper  value  for  n,  owing  to  the  non- 
uniform  character  of  the  interior  surface  of  the  sewer,  make  a 
refinement  of  calculations  out  of  keeping  with  the  data  used. 
Moreover,  in  the  case  of  vitrified  clay  or  concrete  pipe  the 


64 


SEWERAGE. 


TABLE  No.  11. 

VELOCITY    AND    DISCHARGE    IN    SEWERS    4    TO    36    INCHES   DIAMETER. 

Velocity  in  Feet  per  Second;  Discharge  in  Cubic  Feet  per  Minute;  Sewers  Flowing 

Full. 

(Formula  V  =  c   ^~RS\  c  calculated  by  Kutter's  formula,  with  n  =  .013.     Q  —  6oal'.) 


Grade  of 
Sewer. 

4-inch 

6-inch 

8-inch 

lo-inch 

i2-inch 

iS-inch 

i8-inch 

V 

Q 

V 

Q 

V 

Q 

V 

Q 

V 

Q 

V 

Q 

V 

Q 

.1 

5-75 

30.13 

7-99 

94.10 

10.04 

210.3 

11.94 

39°.  8 

13-73 

647.0 

16.24 

1196.0 

18.59 

I97L5 

.05 

4.06 

21.28 

5-64 

66.48 

7.09 

148.6 

8.43 

276.1 

9.70 

457-1 

11.48 

845.0 

13.13 

1393.0 

.04 

3.63 

1903 

5-05 

59-45 

6.34 

132.9 

7-54 

246.9 

8.65 

407.8 

10.26 

755-6 

11.74 

1244.0 

•03 

3-15 

16.47 

4-25 

50.01 

5-49 

115.0 

6-53 

213.7 

7.51 

353-9 

8.89 

654.4 

10.17 

1078.0 

02 

2-57 

13-44 

3.56 

42.00 

4.48 

93.90 

5-33 

174.5 

6.13 

289.0 

7.25 

534-2 

8.30 

880.4 

,01 

1.82 

9-50 

2.52 

29.  70 

3-17 

66.38 

3-77 

123.4 

4-33 

204.3 

5.13 

377-8 

5.87 

622.6 

.008 

i.6l 

8.37 

2.25 

26.53 

2.83 

59.35 

3-37 

110.3 

3.87 

182.6 

4-59 

337-7 

5-25 

556.8 

.OO6 

1.38 

7.18 

1-95 

23.00 

2-45 

51.39 

2.92 

95-55 

3-35 

158.2 

3-97 

292.5 

4-55 

482.3 

.004 

1-59 

18.71 

2.00 

41.85 

2.38 

77.98 

2-74 

129.1 

3-24 

238.3 

3-70 

392.9 

.002 

1.40 

29.38 

1.67 

54.61 

I.9I 

90.40 

2.27 

167.3 

2.60 

275-9 

.OOI 

1.17 

38.41 

1.35 

63-58 

i.  60 

117.7 

1.83 

194-3 

,0009 

I-5I 

111.4 

1-73 

183.9, 

.0008 

1.63 

I73-I 

.0007 

1.52 

161.2 

For«  =  .on        .012        .013        .015        .017 
Multiply  V  or  Q  by  1.20        1.09        i.oo        0.84        0.73 


FLOW  IN  SEWERS. 


TABLE  No.  11.  —  Continued. 

VELOCITY    AND    DISCHARGE    IN    SEWERS    4    TO    36    INCHES  DIAMETER, 

Velocity  in  Feet  per  Second  ;    Discharge  in  Cubic  Feet  per  Minute  ,    Sewers- 

Flowing  Full. 


(Formula  V  =  c  ylRS  ;    c  calculated  by  Kutter's  formula,  with  «  =  .013.     Q  =  6oaV.) 


Grade  of 
Sewer. 

20-inch 

22-inch 

24-inch 

3o-inch 

33-inch 

36-inch 

V 

Q 

V 

Q 

V 

Q 

V 

Q 

V 

Q 

V 

Q 

12920 

.1 

2O.O8 

2628 

21.51 

3407 

22.91 

4319 

26.84 

7905 

28.69 

IO22O 

30.46 

.05 

14.18 

1857 

15.20 

2407 

16.19 

3052 

18.97 

5586 

20.27 

7225 

21.54 

9136 

.04 

12.69 

1661 

13.59 

2153 

14.47 

2729 

16.96 

4995 

18.13 

6461 

19.26 

8171 

•03 

10.98 

1433 

11.77 

1864 

12.53 

2363 

14.69 

4325 

15.70 

5595 

16.68 

7075 

,02 

8.97 

1174 

9.61 

1522 

10.23 

1930 

11.99 

3532 

12.82 

4568 

13.62 

5777 

.or 

€-34 

830 

6.79 

1076 

7.24 

1396 

8.48 

2497 

9.06 

3230 

9.63 

4085 

.008 

5-67 

742 

6.07 

962 

6.47 

1220 

7.58 

2233 

8.  ii 

2889 

8.61 

3653 

.006 

4.91 

643 

5.26 

833 

5.60 

1057 

6-57 

1934 

7.02 

2502 

7.46 

3164 

.004 

4.00 

524 

4.29 

679 

4-56 

860 

5.35 

1576 

5.72 

2040 

6.08 

2580 

.002 

2.81 

368 

3-01 

477 

3-21 

605 

3.76 

1109 

4.02 

1434 

4.28 

1814 

.001 

1.98 

259 

2.12 

336 

2.26 

427 

2.66 

782 

2.84 

1012 

3.02 

1281 

.0009 

I.87 

245 

2.OI 

3i8 

2.14 

404 

2.51 

74i 

2.69 

959 

2.86 

1213 

.0008 

l.76 

231 

1.89 

299 

2.02 

380 

2-37 

697 

2-53 

902 

2.69 

1141 

.0007 

1.64 

215 

1.76 

279 

1.88 

354 

2.  2O 

650 

2.36 

841 

2.51 

1065 

.0006 

l.5i 

198 

1.63 

258 

1-73 

327 

2.04 

600 

2.18 

777 

2.32 

984 

.0005 

I.48 

234 

1.58 

298 

1.86 

546 

1.99 

708 

2.  II 

896 

.0004 

1.32 

208 

1.40 

265 

1.65 

486 

1-77 

630 

1.88 

798 

.0003 

1.20 

227 

1.40 

413 

1-52 

54i 

1.62 

686 

.0002 

0.96 

1  86 

I.I3 

335 

1.22 

435 

1.30 

552 

66 


SE IV ERA  GE. 


TABLE    No.    12. 


VELOCITY    AND    DISCHARGE    IN    SEWERS    33    INCHES    TO    IO    FEET 

DIAMETER. 

Velocity  in  Feet  per  Second;  Discharge  in  Cubic  Feet  per  Minute;  Sewers 

Flowing  Full. 

(Formula  V  =•  c  ty ' RS  ;  c  calculated  by  Kutter's  formula,  with  «  =  .015.     Q  =  6oaV.) 


Grade  of 
Sewer. 

33-inch 

36-inch 

42-mch 

4-foot 

V 

Q 

v 

Q 

V 

Q 

V 

Q 

•05 

17.17 

6120 

18.27 

7750 

20.37 

11765 

22.36 

16865 

.04 

15.36 

5473 

16.34 

6930 

18.21 

10517 

20.00 

15080 

-03 

I3-30 

4733 

14.15 

6000 

15.77 

9108 

13-31 

13057 

.02 

10.85 

3868 

11.55 

4900 

12.88 

7437 

I4.I3 

10658 

,01 

7.68 

2735 

8.16 

3464 

8.90 

5258 

9-99 

7537 

.008 

6.86 

2444 

7.30 

3096 

8.14 

4700 

8.93 

6738 

.006 

5-94 

2115 

6.32 

2679 

7.04 

4067 

7-73 

5832 

.004 

4.84 

1726 

5.15 

2186 

5.75 

3243 

6.31 

4759 

.002 

3-41 

1216 

3.63 

1540 

4-05 

2339 

4-45 

3354 

.001 

2.40 

856 

2.52 

1085 

2.85 

1648 

3-13 

2365 

.OOOg 

2.27 

Bio 

2.42 

1027 

2.70 

1561 

2.97 

2240 

.0008 

2.14 

763 

2.28 

967 

2-55 

1470 

2.80 

2110 

.OOO7 

2.OO 

713 

2.13 

903 

2.38 

1373 

2.61 

1972 

,OOO6 

1.85 

658 

1.97 

834 

2.  2O 

1269 

2.42 

1822 

.0005 

1.68 

598 

1.79 

759 

1-95 

1128 

2.20 

1658 

.0004 

1.49 

532 

1.59 

675 

1.78 

1028 

1.96 

1477 

.0003 

1.28 

457 

1.37 

580 

1-53 

883 

$-68 

1270 

.0002 

1.23 

712 

1.36 

1026 

.OOOI5 

1.16 

878 

For  n=. on       .012      .013      .015       .017 
Multiply  V  or  Q  by  1.43      1.29      1.19      i.oo      0.87 


FLOW  IN   SEWERS. 


67 


TABLE    No    12.— Continued, 

VELOCITY    AND    DISCHARGE    IN    SEWERS    33    INCHES    TO     IO    FEET 

DIAMETER. 

Velocity  in  Feet  per  Second;  Discharge  in  Cubic  Feet  per  Minute;  Sewers 

Flowing  Full. 
(Formula  V  =  c  \ ' RS  ;  c  calculated  by  Kutter's  formula,  with  n  —  .015.     Q=  6o«F.) 


Grade  of 
Sewer. 

5-foot 

6-foot 

8-foot 

io-foot 

V 

Q 

V 

Q 

V 

Q 

V 

Q 

•05 

26.05 

30700 

.04 

23.30 

27450 

26.34 

44690 

-03 

20.17 

23765 

22.81 

38700 

.02 

16.47 

1940S 

18.62 

31600 

22.53 

67965 

26.03 

122700 

.OI 

11.64 

I37I7 

13.17 

22345 

15-93 

48050 

18.41 

86755 

,008 

10.41 

12267 

11.78 

19980 

14.25 

42970 

16.46 

77590 

,006 

9.01 

10617 

10.  19 

17295 

12-33 

37200 

14.25 

67175 

,004 

7.36 

8665 

8.32 

14113 

10.07 

30370 

11.63 

54840 

,002 

5-19 

6110 

5.87 

9956 

7-10 

21435 

8.21 

38720 

,OOI 

3-66 

43ii 

4.14 

7030 

5-02 

15150 

5.81 

27380 

,0009 

3-47 

4083 

3-92 

6659 

4.76 

14353 

5-51 

25960 

.0008 

3-27 

3849 

3-70 

6276 

4.49 

13533 

5-19 

24475 

.0007 

3-05 

3597 

3.46 

5870 

4.20 

12660 

4.86 

22895 

.0006 

2.82 

3326 

3.20 

5429 

3-88 

11710 

4.50 

21195 

.0005 

2.57 

3028 

2.92 

4946 

3-54 

10675 

4.  10 

19325 

,0004 

2.29 

2700 

2.60 

4411 

3.16 

9532 

3.66 

17267 

.0003 

1.97 

2324 

2.24 

3801 

2.73 

8228 

3-17 

14927 

.0002 

i.  60 

1882 

1.82 

3083 

2.22 

6694 

2.58 

12168 

.00015 

i-37 

1615 

1-56 

2650 

1-93 

5820 

2.23 

10510 

.00012 

1-39 

2353 

1-70 

5i37 

1.99 

9375 

.00010 

i-55 

4672 

1.81 

8542 

.000095 

1.25 

3783 

1-77 

8320 

.  000090 

1.72 

8096 

68  SEWERAGE. 

market  sizes  must  in  the  end  be  those  selected,  and  there  is 
a  considerable  jump  between  the  capacities  of  consecutive 
sizes.  For  instance,  an  8-inch  pipe  on  a  \%  grade  will  dis- 
charge about  498  gallons  per  minute  when  running  full;  a 
lo-inch  pipe  running  full  with  the  same  grade  will  discharge 
about  925  gallons  per  minute,  and  a  12-inch  pipe  about  1530 
gallons  per  minute.  For  this  reason  it  is  sufficiently  accurate 
and  often  more  convenient  to  use  curves  plotted  from  the 
tables,  having  the  grade  and  corresponding  velocity  or  dis- 
charge as  coordinates,  from  which  the  flow  through  any  cus- 
tomary size  of  sewer  at  any  practicable  grade  can  be  found  at 
a  glance  and  with  as  great  accuracy  as  is  required  for  ordinary 
use.  Such  a  diagram  can  be  readily  prepared  on  a  sheet  of 
cross-section  paper,  a  curve  being  drawn  for  the  velocity  and 
another  for  the  discharge  of  each  size  of  sewer. 

It  is  now  generally  considered  that  Kutter's  formula  gives 
somewhat  too  small  values  for  sewers  under  15  or  18  inches 
diameter. 

It  must  be  remembered  that  the  formulas  and  tables  of 
velocity  are  supposed  to  apply  only  when  the  sewage  has 
reached  a  constant  velocity.  Previous  to  this  when  the  fric- 
tion does  not  consume  all  of  h  the  remainder  is  creating 
increments  of  velocity.  Since  the  same  amount  of  sewage 
must  pass  all  sections  of  a  sewer  between  two  inlets,  however, 
it  follows  that,  previous  to  the  flow  obtaining  its  maximum 
and  constant  velocity,  the  depth  of  sewage  must  have  been 
greater,  increasing  up  stream  to  the  point  of  entry.  An 
initial  velocity  of  entrance  in  the  direction  of  the  sewage  flow 
will  reduce  the  amount  and  extent  of  this  non-uniform  flow 
with  larger  cross-section,  but  will  have  little  effect  upon  the 
ultimate  constant  velocity.  If  no  such  initial  velocity  exist 
the  entering  sewage  must,  if  it  be  any  large  percentage  of  the 
capacity  of  the  sewer,  back  up  the  feeding-pipe  through  which 
it  entered  in  order  to  create  additional  head  h. 


UNIVERSITY 


FLOW  IN  SEWERS. 


69 


Fis  the  mean  velocity.  The  effect  of  friction  is  exerted 
along  the  wetted  perimeter  and  grows  less  toward  the  centre 
of  the  stream.  The  surface  of  flow  is  also  retarded  by  friction 
with  the  air,  and  frequently  in  the  case  of  house-sewage  by 
a  greasy  scum  which  floats  upon  the  surface.  The  velocity 
given  is  really  the  volume  of  flow  divided  by  its  area. 

area 


Since  V  varies  as 


/{*)=/; 


it  follows 


^wetted  perimeter/ ' 
that  the  size  of  the  sewer  and  the  shape  of  the  cross-section 
have  considerable  effect  upon  the  velocity  of  a  stream.     The 


maximum    value    of 


area 


for    a    sewer  flowing   full    is 


perimeter 

obtained,  we  learn  from  geometry,  by  making  the  cross- 
section  circular;  that  is,  for  pipes  of  the  same  area,  but  differ- 
ent shapes  of  cross-section,  flowing  full,  the  circular  gives  the 
largest  R.  But  this  is  not  generally  true  when  the  sewer  is 
not  flowing  full. 

If  we  examine  the  effect  of  depth  of  flow  in  a  given  cir- 
cular sewer  upon  the  value  of  R  we  find  that  if  the  depth 

d  =  —  (D  equalling  the  diameter  of  the  sewer)  a  =  .3927^', 

p  -—  i. 5 708 A  and  R  —  0.25/7.  If  the  depth  =  D  we  find 
a  =  0.7854^,  /  =  3. 1416/7,  and  R  =  o.2$D  as  before. 

TABLE  No.  13. 


d 
Depth. 

Wetted 
Perimeter. 

a 
Area  of 
Flow. 

R 
Hydraulic 
Radius. 

»Vx 

By  Kutter's  Formula. 

Corrected  Propor- 
tional Velocities. 

Corrected  Propor- 
tional Discharge. 

Full,  i.o 

3-I42 

0.7854 

0.250 

.00 

.00 

1.  000 

0.95 

2.691 

0.7708 

0.286 

.07 

.11 

1.068 

0.9 

2.498 

0-7445 

0.298 

.09 

•15 

1.073 

0.8 

2.214 

0.6735 

0.304 

.10 

.16 

0.98 

0.7 

1.983 

0.5874 

0.296 

.08 

.14 

0.84 

0.6 

.772 

0.4920 

0.278 

05 

1.  08 

0.67 

0-5 

•571 

0.3927 

0.250 

.00 

1.  00 

0.50 

0.4 

.369 

0.2934 

0.214 

0.93 

0.88 

0-33 

0-3 

•159 

O.igSl 

0.171 

0.83 

0.72 

0.19 

0.25 

.047 

0.1536 

0.146 

0.76 

0.65 

0.14 

O.2 

0.927 

0.1118 

O.I2I 

0.69 

0.56 

0.09 

O.I 

0.643 

0.0408 

0.0635 

0.50 

0.36 

0.03 

SEWERAGE. 


As  the  depth  of  the  sewage  decreases  from  that  of  half  the 
diameter  the  area  decreases  more  rapidly  than  does  the 
wetted  perimeter,  and  consequently  'R  decreases  more  and 
more  rapidly  as  the  depth  diminishes.  The  above  table 
shows  this  very  plainly.  The  diameter  is  here  taken  as  unity, 
the  sewer  circular. 

The  formula  for  R  for  circular  sewers  for  any  given  depth 
of  flow  is 


area 


360 


—  r   sin  a  cos  a 


wetted  perimeter 

1 80  sin  a  cos 


2a 
360 


X    27T7- 


=  ;(- 


in  which  r  =  the  radius  of  the  sewer  perimeter; 

a  =  the  number  of  degrees  in  the  angle  whose  cosine 

r  —  the  depth  of  flow 
is  . 

For  the  egg-shaped  sewer  (see  Art.  24)  somewhat  different 
values  are  found. 

TABLE  No.   14. 

EGG-SHAPED    SEWER. 
(D  =  horizontal  diameter  ;  //  =  vertical  diameter.) 


By  Kutter's  Formula. 

d 

d 
in  parts 
oiH. 

d 
in  parts 
of  D. 

P 

in  parts 
oiD. 

a 
in  parts 
of  D*. 

/? 
in  parts 
of  D. 

i.8S87/ff 

Corrected 
Propor- 
tional 

Corrected 
Propor- 
tional 

in  Circular 
Sewer 
in  parts  of 

Velocities. 

Discharge. 

D* 

Full  i.ooo 

1-50 

3-965 

I.I485 

0.2897 

I.OOO 

I.OO 

I.OO 

1.209 

0.667 

1.  00 

2-394 

0.7558 

0.3157 

1.045 

1.  06 

0.69 

0.750 

0-333 

O.5O 

1-374 

0.2840 

o.  2066 

0.846 

0.77 

0.18 

0-354 

0.267 

0.40 

I-I59 

0.20485 

o.  1  768 

0.781 

0.70 

0.12 

0.284 

O.22O 

0-33 

1.  012 

0.15510 

0.1532 

0.727 

0.63 

O.oSl 

O.228 

O.2OO 

0.30 

0-937 

O.I347I 

0.1437 

0.704 

0.60 

0.064 

0.214 

0.133 

0.20 

0.706 

0.07497 

o.  1062 

0.606 

0.49 

0.030 

0.141 

0.067 

0.10 

0.463 

0.0279 

0.06026 

0.455 

0.33 

0.008 

0.075 

0.033 

O.05 

0.321 

0.0102 

0.03177 

0-331 

0.23 

O.OO2 

0.039 

*  To  give  equal  discharge  in  circular  sewer  of  same  capacity— i.e.,  one  whose  diameter  = 
1.909  D. 


FLOW  IN  SEWERS.  7 1 

By  Table  No.  13  it  is  seen  that  when  a  circular  sewer  is 
half  full  the  wetted  perimeter  and  area  of  flow  are  each  half 
of  that  for  a  full  sewer.  When  the  depth  is  but  J  the 
diameter,  however,  the  wetted  perimeter  is  -J,  the  area  of -flow 
less  than  \,  and  R  about  ^  that  of  a  full  sewer;  and  when  the 
depth  is  y1^  the  wetted  perimeter  is  about  ^,  the  area  -J-g-,  and 
R  about  \  that  of  a  full  sewer. 

In  the  last  two  columns  we  have  the  proportional  veloci- 
ties and  discharges  for  various  depths  of  flow,  with  allowance 
made  for  variations  in  c,  calculated  by  Kutter's  formula,  with 
sufficient  accuracy  for  ordinary  use.  The  fifth  column  shows 
proportional  velocities  if  c  is  considered  as  not  affected  by 
changes  in  R.  A  comparison  of  the  fifth  and  sixth  columns 
shows  the  effect  upon  the  coefficient  c  of  variations  in  Rr 
since  if  c  =  x  for  a  full  sewer  for  one  .2  full  it  equals  ||;r 
and  for  one  .8  full  \\^x. 

Reference  to  Table  No.  13  shows  that  if,  in  a  circular 
sewer  with  a  depth  of  flow  of  J  the  diameter,  the  velocity  is 
i£  feet  per  second  (the  minimum  velocity  of  flow  ordinarily 
permissible  for  house-sewers),  in  the  same  sewer  flowing  full 
the  velocity  will  be  2.3  feet  per  second.  It  also  appears  from 
this  table  that  the  greatest  velocity  is  attained,  not  when  the 
sewer  is.  flowing  full,  but  when  the  depth  is  .81  of  the  diam- 
eter, and  that  the  maximum  discharge  occurs  when  the  depth 
is  .9  of  the  diameter.  From  this  it  follows  that  a  circular 
sewer  can  never  flow  full  unless  under  a  head. 

The  tables  Nos.  n  and  12  for  flow  in  sewers  give  the 
velocity  and  discharge  for  full  sewers  only,  the  velocity  being 
the  same  for  a  sewer  half  full,  while  the  discharge  is  one  half 
as  great.  They  do  not  give  the  maximum  capacity  of  the 
sewer,  which  is  theoretically  1.07  times  that  given;  but  the 
velocity  and  discharge  for  sewers  flowing  full  are  most  con- 
venient for  use  and  are  on  the  safe  side  of  exact  accuracy. 

Where  it  is  desired  to  obtain  the  velocity  or  discharge  of 


72  SEWERAGE. 

a  sewer  flowing  partly  full  the  tables  can  be  entered  with  the 
quantities  corresponding  to  the  other  conditions,  the  velocity 
or  discharge  of  the  sewer  as  if  it  were  flowing  full  obtained, 
and  such  part  of  this  taken  as  is  indicated  by  the  above  table 
for  the  given  depth.  For  instance,  if  it  is  desired  to  find  the 
discharge  of  a  lO-inch  circular  sewer,  grade  I  :  200,  when  the 
depth  of  flow  is  0.4  the  diameter,  we  find  from  the  table  that 
the  discharge  if  running  full  would  be  about  650  gallons  per 
minute;  we  multiply  this  by  0.33  and  obtain  214  gallons,  the 
volume  required.  Or,  given  the  volume,  215  gallons,  and  the 
grade,  I  :  200,  to  find  the  depth  of  flow:  we  find  the  flow  of 
a  full  sewer,  650  gallons,  divide  215  gallons  by  this,  obtaining 
-J,  and  find  the  depth  corresponding  to  this  proportion  of  the 
discharge,  or  0.4. 

The  velocity  obtained  by  the  formula  or  from  the  table 
is  that  for  a  straight  pipe  of  a  uniform  cross-section  and 
condition  of  surface.  In  a  system  of  sewers  there  are 
numerous  curves,  irregularities  of  surface,  manholes,  house- 
branches,  etc.,  each  of  which  may  exert  a  retarding  in- 
fluence upon  the  sewage.  It  is  thought  that  there  is  no  ap- 
preciable diminution  of  velocities  in  a  curve  whose  radius  is  at 
least  5  times  the  diameter  of  the  sewer.  Weisbach's  formula 
for  loss  of  head  in  curves  is 

caV* 
11578' 

fr\* 

in  which  c  =  .131  +  1 . 8471-7-  ]  ; 


r  —  radius  of  pipe; 

£  =       "      4<    bend; 

a  =  angle  in  degrees; 

V •=.  velocity  in  feet  per  second; 

h  =  head  in  feet  necessary  to  overcome  resistance  of 

curve. 
From  the  above  formula  we  find  that  if 


FLOW  IN  SEWERS.  73 

.2       .3       .4      .  5       .6       .7       .8         .9       i.o 

then 

^  =  .131    .138    .158    .206   .294  .440  .661   .977   1.408   1.978 

As  an  example,  assume  a   lO-inch  pipe,  or  r  =  0.42  feet, 

that  b  =  2   feet,  that  a  =  90°,  that    V=  3  feet.     Then  h  = 

,  138  X  90  X  9 

—5 —   -  =  .0097  feet,  or  less  than  -J  inch.      This  result 
11575 

is  not  sufficiently  large  to  materially  affect  the  design.  It 
represents  the  case  of  a  junction  between  sewers  made  by  a 
curve  in  a  manhole  (see  Plate  VIII,  Fig.  5).  This  formula, 
however,  does  not  apply  to  the  foaming  or  impact  created  by 
an  angle.  A  very  considerable  loss  of  head  may  result  from 
this,  and  consequently  sharp  bends  should  be  avoided  unless 
it  is  desired  to  reduce  the  velocity. 

The  obstructions  to  flow  offered  by  manholes,  house-con- 
nections, etc.,  can  be  almost  entirely  avoided  by  careful 
designing  and  construction.  That  due  to  roughness  of  the 
material  of  construction  should  also  be  kept  low,  but  will 
necessarily  be  considerable.  This  obstruction  should  be 
allowed  for  in  the  formula  by  modifying  the  value  of  c  through 
the  different  values  of  n. 

ART.  22.     LIMITS  OF  VELOCITY. 

The  formula  for  the  quantity  of  sewage  which  will  flow 
through  a  given  sewer  per  second  is  Q  =  Va,  in  which  a  is  the 
area  of  the  stream  flowing.  It  would  appear  that,  given  <2, 
Fand  a  could  take  any  value  so  long  as  Va  =  Q.  a  is,  how- 
ever, limited  in  its  maximum  by  economic  considerations,  also 
sometimes  by  practical  ones  (see  Art.  23).  Falso,  although, 
if  pure  water  were  the  material  flowing  through  the  sewers,  it 
might  vary  from  o  to  infinity,  is  limited  within  a  compara- 
tively narrow  range  by  the  character  of  ordinary  sewage. 

House-sewage    contains    some   matter    which    is    slightly 


74  SEWERAGE. 

heavier  than  water,  also  much  which  is  lighter;  the  former 
tends  to  settle  in  the  bottom  of  a  sewer,  the  latter  to  collect 
along  the  edges  of  the  stream.  Ashes,  garbage,  clothing,  and 
other  refuse  matter  should  be  kept  out  of  the  sewers  by  laws 
rigidly  enforced,  but  in  spite  of  all  precautions  such  material 
will  at  times  reach  them.  Dirt  and  sand  frequently  enter 
house-sewers  through  the  ventilation-holes  in  manhole-heads 
or  through  defective  joints  in  the  sewer.  As  no  system  is 
perfect  or  perfectly  managed,  provision  should  be  made  for  a 
certain  amount  of  such  matter.  It  is  found  that  if  the 
velocity  of  a  stream  be  sufficiently  great  matter  suspended  in 
the  water  will  not  be  deposited,  but  a  retarding  of  the  velocity 
at  any  point  may  cause  a  formation  of  deposits  there.  Ex- 
periments have  been  made  to  determine  the  velocities  neces- 
sary for  flowing  water  to  render  it  capable  of  transporting 
matter  of  various  sizes  and  densities,  though  usually  earth, 
sand,  gravel,  and  stones  have  been  used.  The  results 
obtained  by  DuBuat  are  those  usually  quoted,  and  are  given 
as  being  approximately  correct  for  channels  of  uniform  cross- 
section.  The  velocities  are  those  sufficient  to  move  the  par- 
ticles along  the  bottom  of  the  channel  and  are  in  feet  per 

second. 

TABLE  No.  15. 

MATERIALS    MOVED    BY  WATER   FLOWING    AT    DIFFERENT  VELOCITIES. 
Material.                                           Bottom  Velocity.  Mean  Velocity.. 

Pottery-clay 0.3  0.4 

Sand,  size  of  anise-seed 0.4  0.5 

Gravel,  size  of  peas , 0.6  0.8 

"          "     "    beans 1.2  1.6 

Shingle,  about  I  inch  in  diameter 2.5  3.3 

Angular  stones,  about  \\  inches  in  diameter 3.5  4.5 

Other  experiments  have  given  slight  variations  from  these 
figures,  but  they  are  sufficiently  accurate  for  ordinary  use. 
It  must  be  remembered  that  they  apply  to  loose  material  only. 
Where  clay  or  sand  has  formed  a  compact  deposit  in  a  sewer 
many  times  these  velocities  may  be  required  to  move  it. 
Just  which  of  these  or  similar  materials  the  sewage  should  be 


FLOW  IN  SEWERS.  75 

given  sufficient  velocity  to  hold  suspended  is  a  question. 
But  it  has  been  found  in  practice  that  an  actual  velocity  of  i£ 
feet  per  second  will  ordinarily  suffice  to  prevent  deposits 
where  house-sewage  alone  is  admitted. 

Where  storm-water  from  the  streets  is  admitted  to  the 
sewers  clay,  sand,  gravel,  leaves,  etc.,  as  well  as  lighter  matter 
are  washed  through  the  inlets.  The  velocities  in  these  sewers 
should  be  sufficient  to  prevent  the  deposit  of  such  material, 
which  velocity,  according  to  the  table  given  above,  would 
needs  be  about  3.5  feet  per  second. 

The  velocity  given  for  house-sewers — if  feet  per  second 
— -is  that  which  should  be  maintained  as  a  minimum  by  the 
ordinary  minimum  daily  flow;  that  for  storm-sewers — 3.5  feet 
per  second — is  the  least  which  should  be  attained  in  time  of 
storms. 

The  average  daily  flow  in  house-sewers  may  be  taken 
(Art.  14)  as  %  of  the  maximum  to  be  provided  for,  and  the 
ordinary  minimum  as  J  of  this.  At  night-time,  when  the 
absolute  minimum  usually  occurs,  the  sewage  is  composed  of 
comparatively  pure  water  and  a  lessened  velocity  due  to  a 
shallower  flow  will  not  be  particularly  detrimental,  -f-  of  the 
maximum  volume  for  which  the  sewer  is  designed  may  there- 
fore be  assumed  as  that  for  which  the  velocity  should  be 
if  feet  per  second.  For  reasons  to  be  given  (Art.  23)  a  house- 
sewer  is  usually  designed  to  be  50$  to  ioofo  larger  than 
required  by  the  assumed  volume  of  sewage,  so  that  the  ordi- 
nary minimum  can  be  taken  as  being  ^  to  -J-  of  the  capacity  of 
the  sewer.  Reference  to  Table  No.  13  shows  that  this 
quantity  is  carried  when  the  depth  of  flow  in  the  sewer  is  .25 
to  .3  the  diameter  and  when  the  velocity  is  .6$  to  .72  that 
for  a  sewer  flowing  full.  It  follows  from  this  that  the  grade 
of  a  house-sewer  should  be  such  that  the  velocity  when  flow- 
ing full  is  at  least  -jr-  to  -1— ,  or  2.3  to  2. 1  feet  per  second. 


76  SEWERAGE. 

In  the  case  of  storm-sewers,  which  carry  no  house-sewage 
and  are  thus  dry  for  a  large  portion  of  the  time,  it  may  be 
assumed  that  in  general  any  storm  which  will  wash  any  con- 
siderable amount  of  gravel  and  dirt  into  them  will  require  at 
least  one  third  of  the  capacity  of  the  sewer.  Such  grades 
should  therefore  be  given  these  as  will  cause  a  velocity  of  at 
least  3.5  feet  per  second  when  the  sewer  is  flowing  one 
third  full,  or  4  feet  when  flowing  full.  Smaller  showers, 
which  will  give  less  depth  of  water  in  the  sewer,  it  may 
likewise  be  assumed  will  contribute  only  such  matter  as  is 
transported  by  less  velocities. 

It  may  in  some  cases  be  necessary  to  construct  sewers 
giving  somewhat  lower  velocities  than  these,  but  this  should 
be  only  after  careful  consideration  of  the  problem.  House- 
sewers  should  never  be  designed  with  grades  giving  a  less 
velocity  than  2  feet  per  second  when  flowing  full,  nor  storm- 
sewers  with  those  giving  less  than  3  feet. 

Where  a  combined  sewer  is  in  question — i.e.,  one  which 
daily  carries  house-sewage,  but  which  also  has  sufficient 
capacity  for  and  acts  as  a  storm-sewer — the  requisite  velocity 
must  be  obtained  for  both  house-  and  storm-sewage.  But 
except  in  very  unusual  instances  a  grade  which  will  meet  the 
requirements  of  house-sewage  will  more  than  satisfy  the 
demands  of  storm-water  transportation.  For,  since  the  maxi- 
mum amount  of  house-sewage  per  second  per  acre  in  a  resi- 
dence district  will  be  about ~ o"? —  -°22  cubic  feet, 

7.4.0  X  00400 

while  the  storm-water  from  'such  an  area  may  be  3  cubic  feet 
per  second,  or  140  times  as  great,  if  a  circular  sewer  is 
designed  to  give  a  velocity  of  i£  feet  when  it  is  carrying  .007 
of  its  full  capacity  its  velocity  when  flowing  full  will  be  about 
9  feet,  or  more  than  twice  the  desired  velocity;  while  with  an 
egg-shaped  sewer  under  the  same  conditions  a  velocity  of  4.7 
feet  when  flowing  full  is  obtained. 


FLOW  IN  SEWERS.  77 

The  subject  of  maximum  velocities  has  received  but  little 
attention,  probably  because  the  dangers  connected  with 
excessive  velocities  are  not  so  great  as  those  resulting  from  a 
too  slow  rate.  Such  dangers  do  exist,  however.  The  more 
immediate  one  is  that  the  consequent  shallowness  of  the 
current  which  would  in  many  cases  result  would  occasion  the 
deposit  of  the  larger  floating  solids,  which  may  result  in 
obstinate  obstructions  in  the  sewer.  In  the  mains  this  can  be 
obviated  by  reducing  the  size  of  the  sewer  to  the  point  where 
the  necessary  depth  is  obtained.  But  it  is  usually  not  in  the 
mains  but  in  the  branches  that  steep  grades  are  possible.  To 
reduce  the  sewer  to  such  a  size  as  would  give  any  consider- 
able depth  to  the  daily  flow  on  very  steep  grades  would  call 
for  a  diameter  much  below  that  usually  adopted  as  a  mini- 
mum. An  8-inch  sewer  whose  grade  is  o.  I  gives  a  theoretic 
velocity  of  10.04  feet  per  second  when  flowing  full.  To 
secure  a  flow  in  this  pipe  having  an  average  depth  of  4  inches 
would  require  the  sewage  from  a  population  of  6500.  In 
general  it  may  be  said  that  the  ordinary  depth  of  flow  in  any 
sewer  should  not  be  less  than  2  inches,  nor  should  it  be 
less  than  £  the  radius  of  the  invert,  since  if  it  is  so  there 
is  much  more  danger  of  deposits  forming  along  the  edges 
and  even  in  the  centre  of  the  stream.  It  will  sometimes  be 
impossible  to  meet  this  requirement  fully,  but  it  should  be 
kept  in  mind  as  extremely  desirable. 

Another  objection  to  too  great  velocity  is  the  danger  of 
attrition  of  the  sewer-invert  by  the  scouring  action  of  sand, 
stones,  etc.,  swept  rapidly  over  it.  In  brick  sewers  this 
objection  is  frequently  and  successfully  met  by  lining  the 
invert  with  granite  blocks.  A  5j-foot  two-ring  brick  sewer 
in  Baltimore,  25  years  old,  was  recently  found  with  its  invert 
in  one  place  cut  completely  through  for  a  width  of  12  to  15 
inches  and  badly  worn  for  a  height  of  2  feet,  and  many  other 
places  were  only  a  little  less  damaged.  In  Omaha's  brick 


78  SEWERAGE. 

sewers  the  wear,  which  is  usually  18  to  24  inches  wide, 
became  2  to  3  inches  deep  in  12  years.  In  both  cities  ordi- 
nary brick  was  used,  but  was  replaced  with  stone  blocks. 

The  first  objection  is  the  serious  one,  since  the  time  taken 
to  wear  out  a  sewer-invert  must  be  considerable  if  good 
material  is  used,  and  replacing  it  is  a  matter  of  expense  only. 
But  the  forming  of  deposits  in  the  sewer  endangers  the  health 
of  the  community. 

It  is  difficult  to  set  a  maximum  limit  to  the  velocity  allow- 
able, but  it  may  generally  be  taken  as  from  8  to  12  feet  per 
second.  From  3  to  5  feet  per  second  is  probably  the  most 
desirable  velocity. 

ART.  23.     SIZE  OF  SEWERS. 

If  a  house-sewer  were  constructed  to  exactly  meet  the 
theoretical  requirements  as  above  outlined  it  would  contin- 
ually increase  in  size  from  the  head  to  the  outlet,  by  a  small 
increment  below  each  house-connection,  by  a  larger  one  below 
each  tributary  branch  or  lateral;  but  between  the  first  two 
connections  it  should  be  of  sufficient  size  to  carry  the  sewage 

of  one   house   only,    which   would   be   about    - — 8~v   86 

=  .0016  cubic  feet  per  second,  which  at  a  velocity  of  2.5  feet 
per  second  would  call  for  a  pipe  of  .00064  square  feet  area, 
or  -J  inch  diameter. 

This  method  is  not  closely  followed  for  the  reasons  that 
the  data  on  which  are  based  the  calculations  of  volume  of 
sewage  as  well  as  the  formulas  of  flow  cannot  be  exact  enough 
to  warrant  it;  that  the  estimate  of  ultimate  population  may 
be  exceeded;  that  the  per  capita  water-consumption  may 
increase  beyond  the  maximum  assumed,  factories  or  other 
large  contributors  of  sewage  locate  at  points  where  they  were 
not  expected,  or  for  some  other  cause  the  amount  of  sewage 


FLOW  IN  SEWERS.  79 

reaching  any  lateral  may  be  largely  exceeded.  This  excess 
can  be  allowed  for  in  a  general  way  only,  but  it  is  advisable  to 
design  the  laterals  of  a  capacity  double  that  calculated,  par- 
ticularly since  the  cost  is  not  thereby  largely  increased,  and 
the  velocity  in  a  sewer  flowing  half  full  is  as  great  as  that  in 
one  flowing  full. 

The  house-sewer  mains  need  not  have  so  great  an  excess 
of  size,  since  they  carry  the  sewage  from  many  laterals,  and 
it  is  not  probable  that  all  these  will  receive  double  the  calcu- 
lated amounts  of  sewage.  It  will  probably  be  sufficient  to 
increase  these  by  50$  of  the  estimated  capacity.  The  volume 
of  sewage  reaching  the  trunk  or  outlet  sewer  can  be  still  more 
closely  calculated,  and  an  increase  of  25$  may  be  made  as 
giving  it  sufficient  capacity,  although  it  would  probably  be 
better  to  add  50$  here  also,  the  additional  cost  being  slight  in 
most  cases. 

With  this  increase  the  head  of  each  lateral  would  still  be 
less  than  \  inch  in  diameter.  This  would  be  too  small  to 
adopt  in  practice  for  several  reasons:  because  an  individual 
house  will  contribute  sewage  at  occasional  maximum  rates  far 
exceeding  175$  of  their  daily  average;  because  a  very  small 
sewer  would  be  too  frequently  stopped  by  pieces  of  paper, 
cloth,  or  other  legitimate  sewage  matter;  and  because  it  would 
be  too  difficult  of  access  for  inspection  and  cleaning.  The 
last  two  objections  could,  it  is  true,  be  met  theoretically  by 
making  the  house-connection  of  a  size  so  much  smaller  that 
nothing  could  pass  it  which  would  obstruct  the  sewer.  But 
such  construction  would  be  utterly  impracticable. 

There  is  no  particularly  good  reason,  however,  why  a 
house-connection  might  not  be  made  of  2-inch  pipe  and  the 
sewer  of  3-inch  or  4-inch;  and  systems  are  in  existence  and 
reported  working  satisfactorily  where  such  sizes  are  in  use. 
But  such  construction  would  generally  compel  a  change  in  the 
stock  dimensions  of  all  house-plumbing  and  connected  appli- 


80  SEWERAGE. 

ances,  and  give  rise  to  inconveniences  more  than  balancing 
the  saving  in  cost.  A  4-inch  house-connection  is,  however, 
ample  for  any  building  containing  less  than  50  persons  and 
which  contributes  only  ordinary  house-sewage  (see  Art.  82). 

The  sewer  might,  then,  where  the  grade  is  quite  steep,  be 
constructed  as  a  4-inch  pipe  from  the  head  to  such  point  as 
the  calculations  fix  for  an  increase  in  size;  but  it  is  better  to 
make  the  minimum  diameter  6  or  8  inches,  for  then  there 
would  be  less  probability  that  anything  passing  the  house-con- 
nection, in  which  the  velocity  may  be  considerable,  would 
obstruct  the  sewer.  It  is  thought  that  the  weight  of  evidence 
tends  to  show  that  with  4-inch  house-connections  8-inch 
sewers  are  obstructed  much  less  frequently  than  are  6-inch. 
Among  other  reasons  for  this  is  the  fact  that  a  6-inch  stick, 
chicken-bone,  etc.,  will  pass  a  4-inch  trap,  but  an  8-inch  one 
will  not;  and  that  a  6-inch  stick  is  more  apt  to  become 
wedged  across  a  6-inch  pipe  than  across  an  8-inch  one.  Some 
engineers  set  the  6-inch,  more,  probably,  the  8-inch  pipe, 
as  the  minimum  to  be  employed  for  sewers.  In  England 
9  inches  is  generally  the  minimum  size. 

In  the  case  of  storm-sewers  the  only  change  of  conditions 
affecting  the  volume  of  sewage  which  is  likely  to  occur  is  in 
the  imperviousness  of  the  contributing  area.  If  this  is  taken 
at  the  maximum,  as  for  a  business  district,  no  allowance  need 
be  made.  In  any  case  the  allowance  for  change  can  best  be 
made  in  the  selection  of  the  factor  of  imperviousness  and  the 
sewer  built  of  corresponding  capacity.  It  is  probable  that  no 
condition  of  size  or  character  of  tributary  area  will  in  actual 
practice  call  for  a  storm-sewer  of  a  diameter  less  than  10  or 
12  inches.  It  should,  if  possible,  be  of  a  diameter  at  least  as 
great  as  that  of  the  largest  opening  in  the  storm-water  inlets, 
to  prevent  sticks  lodging  across  it. 

A  circular  or  egg-shaped  sewer  is  sometimes  limited  in  size 
by  the  amount  of  covering  necessary  and  the  distance  below 


FLO W  IN  SEWERS.  8 1 

the  street-surface  of  its  invert,  where  this  is  fixed  by  the  eleva- 
tion of  the  outlet  and  the  necessary  grade  from  that  to  the 
point  in  question.  If  the  whole  sewer  at  this  point  be  lowered 
the  grade  and  velocity  become  less  and  the  size  of  the  sewer 
must  be  increased,  thus  raising  the  crown.  The  size  can  be 
reduced  only  by  increasing  the  grade,  which  means  raising 
the  sewer.  Under  these  conditions  the  sewer  can  be  built  as 
an  "  inverted  siphon  "  to  flow  under  a  head  (Art.  38),  two  or 
more  parallel  sewers  can  be  substituted  for  the  one,  or  the 
shape  can  be  modified.  In  adopting  the  last  alternative 
engineers  have  devised  many  forms  which  can  be  generally 
classified  as  those  flattened  on  the  bottom  and  those  flattened 
at  the  top. 

ART.  24.     SHAPE  OF  SEWERS. 

Of  all  possible  shapes  of  sewers  of  equal  area  of  cross-sec- 
tion the  circular  gives  the  greatest  velocity  when  flowing  full 
or  half  full  and,  having  the  shortest  perimeter,  contains  the 
least  material.  Also,  being  devoid  of  angles,  it  offers  little 
opportunity  for  deposits.  For  sewers  intended  to  always  flow 
at  least  half  full  it  is  therefore  the  most  desirable  shape. 
This  is  not  true,  however,  of  a  combined  sewer — that  is, 
one  which  carries  both  house-sewage  and  storm-water — 
for,  as  we  have  seen  (Art.  22),  the  house-sewage  may  occupy 
only  -3-^  of  the  capacity  of  the  sewer  and  have  a  velocity  only 
about  \  as  great  if  a  circular  sewer  be  used.  If  the  sewer, 
considered  as  a  storm-sewer,  be  given  a  grade  adapted  to  a 
velocity  of  4  feet  per  second  when  flowing  full  or  half  full  the 
velocity  of  the  house-sewage  would  be  about  -f  of  a  foot  per 
second.  If  on  the  other  hand  the  grade  be  so  increased 
(which  is  seldom  possible)  as  to  give  the  minimum  house- 
sewage  flow  a  velocity  of  \\  feet  per  second  the  depth  of  this 
flow  would  be  only  about  .02  of  the  sewer  diameter.  Neither 
of  these  conditions  is  permissible  in  a  good  sewerage  system. 


82 


SEWERAGE. 


The  result  of  adopting  too  flat  a  grade  is  shown  by  the 
illustration  (Plate  VII,  Fig.  8)  of  obstructions  in  the  old 
London  sewers,  which  came  to  be  known  as  "  sewers  of 
deposit.'*  These  required  frequent  cleaning,  since  almost 
the  entire  sewage  matter  was  deposited  in  them,  and  became 
very  dangerous  to  the  health  of  the  city.  The  question  thus 
forced  upon  the  attention  of  engineers  was  first  solved  by 
building  in  the  bottoms  of  the  old  sewers  channels  of  much 
shorter  radius  of  curvature  (Plate  VII,  Fig.  7).  These,  by 
increasing  R  and  consequently  F,  as  well  as  the  depth  of  flow 
relative  to  the  invert  radius,  had  the  same  effect  upon  the  flow 


FIG.  2. — EGG-SHAPED  SEWER. 

as  the  use  of  smaller  sewers,  which  they  in  fact  were,  and 
answered  the  purpose,  practically  the  same  design  being  still 
employed  in  Washington,  D.  C.,  and  other  American  cities. 
It  will  be  noticed,  however,  that  there  is  considerable  useless 
material  in  this  design;  also  that  the  bench  on  either  side  of 
the  small  channel  offers  opportunity  for  the  deposit  of 
material,  which  may  there  putrefy.  To  meet  these  objections 
the  egg-shaped  sewer  was  designed  and  is  used  extensively 
for  combined,  and  often  for  storm-water,  sewers.  Several 


FLOW  IN   SEWERS.  83 

proportions  have  been  suggested  and  used,  but  that  most 
frequently  found  in  modern  American  practice  is  represented 
here.  The  diameter  of  a  circular  sewer  having  an  equal  area 
is  1.  209/2.  In  this  sewer 


'    =  O.5A 
eforr=i.$D,  gh  or  r"  =  o.2$D. 


Reference  to  Table  No.  14  shows  that  a  flow  of  yj^  of  the 
full  capacity  of  this  sewer  would  have  a  velocity  about  0.3  as 
great  as  if  the  sewer  flowed  full,  or  85$  greater  than  the  same 
amount  in  a  circular  sewer  of  equal  total  capacity;  also  the 
depth  would  be  about  o.  \D,  or  o.^r".  If  the  velocity  of  the 
house-sewage  in  the  above  be  2\  feet  per  second  (as  it  should 
be)  that  when  the  sewer  were  full  would  be  8  feet  or  more 
per  second.  This  form  does  not,  therefore,  quite  meet  the 
requirements  of  a  combined  sewer,  intended  to  carry  a  run-off 
of  3  inches  from  the  area  drained,  as  to  either  depth  or 
velocity  of  house-sewage.  As  we  shall  see  later,  this  require- 
ment applies  to  lateral  combined  sewers  only,  and  this  design 
is  suitable  for  most  combined-sewer  mains,  whose  maximum 
flow  is  only  \\  or  2  inches  run-off  from  the  drainage-area. 
In  laterals  or  other  sewers,  however,  where  the  proportion  of 
house-  to  storm-sewage  will  be  too  small,  or  for  some  other 
reason  sufficient  velocity  and  depth  for  the  house-sewage 
cannot  be  thus  obtained,  the  adoption  of  an  egg-shaped  sewer 
with  r"  =  %D  or  ^D,  or  a  form  similar  to  that  shown  in  Plate 
VII,  Fig.  2,  is  recommended,  the  purpose  being,  whatever 
the  form  adopted,  to  get  a  satisfactorily  high  value  for  R  for 
the  house-sewage  flow.  Whatever  the  radius  of  invert  the 
grade  must  not  be  less  than  that  which  would  be  required 
by  a  circular  house-sewer  having  a  radius  —  r".  The 
radius  r"  should  be  so  chosen,  also,  that  the  depth  of  house- 

r" 
sewage  will  never  be  less  than    —  .     A  flat   bottom   should 


84  SEWERAGE. 

never  be  used  for  house  or  combined  sewers  unless  the 
sewage  will  always  be  sufficient  to  cover  it  at  least  6  inches 
deep.  Angles  in  the  section  are  to  be  avoided  as  favoring 
deposits.  In  storm-sewers  it  is  advisable  that  the  shape  be 
such  as  to  give  good  velocity  to  small  amounts  of  storm- 
water,  but  the  penalty  of  not  following  this  rule  is  not  so 
serious  as  in  the  case  of  house-sewers. 


CHAPTER   V. 
FLUSHING  AND  VENTILATION. 

ART.  25.     NECESSITY  FOR  FLUSHING. 

IT  is  seen  from  Table  No.  13  that  if  at  any  time  the  flow 
in  a  circular  sewer  becomes  less  in  volume  than  y1^  the  full 
capacity  of  the  sewer  the  depth  becomes  less  than  J  the 
diameter  and  the  velocity  less  than  f  that  for  a  full  sewer. 
If  the  sewer  is  small  the  first  condition  is  apt  to  cause 
deposits  by  the  stranding  of  floating  matter  on  the  edges  or 
even  in  the  centre  of  the  stream ;  if  the  grade  is  near  the 
minimum  the  velocity  becomes  less  than  is  desirable  and 
deposits  result  from  this  cause.  But  a  6-inch  or  8-inch  pipe 
is  usually  the  minimum  size  employed  and  is  carried  up  to  the 
last  house-connection,  from  which  a  quantity  of  sewage  very 
much  less  than  -^  of  the  full  sewer  capacity  is  received.  In 
fact  there  will  be  in  a  residence  district  a  stretch  of  at  least 
400  feet  of  6-inch  or  700  feet  of  8-inch  sewer,  even  at  the 
flattest  allowable  grade,  which  would  be  filled  less  than  -^  of 
its  capacity  by  a  rate  of  175  gallons  per  capita,  and  conse- 
quently where  deposits  are  probable.  The  discharge  from  any 
individual  house  comes  usually  not  in  a  continuous  flow,  how- 
ever, but  in  spurts  of  relatively  large  quantities  separated  by 
considerable  intervals  of  time.  If  we  watch  such  intermittent 
discharge  we  will  find  that  when  the  sewage  enters  an  empty 
sewer  from  the  house-connection  it  flows  both  down  the 
grade  and  also  up  it  for  a  short  distance.  The  latter  portion 

85 


86  SEWERAGE. 

at  the  end  of  the  discharge  also  flows  down  grade,  but  it  has 
probably  carried  with  it  and  left  at  the  upper  limit  of  its  flow 
matter  which  remains  there  to  putresce  and  perhaps  form  the 
beginning  of  an  obstruction.  Beginning  in  the  sewer  at 
practically  nothing  (since  most  of  the  initial  velocity  is 
destroyed  by  foaming),  the  velocity  of  such  discharge  contin- 
ually increases,  and  the  depth  decreases,  with  the  distance 
from  the  point  of  entry.  This  frequently  causes  the  strand- 
ing below  the  house-connection  of  large  floating  matter  which 
is  introduced  from  such  connection,  and  although  successive 
discharges  may  move  this  matter,  each  one  a  little  further 
down  the  sewer,  a  long  cessation  of  them  may  give  it  an 
opportunity  to  become  fixed  in  its  position.  Discharges  from 
connections  higher  up  the  grade  will  tend  to  prevent  these 
deposits,  two  or  more  discharges  occasionally  coming  simul- 
taneously and  uniting  their  volume;  and  generally  the  further 
any  connection  is  from  the  upper  or  dead  end  of  a  branch  the 
less  the  danger  of  its  causing  such  deposits.  In  a  thickly 
settled  district  this  danger  in  the  case  of  6-  or  8-inch  pipe 
becomes  very  small  at  a  point  to  which  there  is  tributary 
1000  to  1500  feet  of  sewer.  If  the  district  is  sparsely  settled, 
however,  the  danger  may  exist  for  many  times  this  length. 

Any  house-sewer,  but  particularly  a  lateral,  is  liable  to 
partial  stoppage  at  times,  due  to  ashes,  sand,  or  other 
material  introduced  through  house-connections,  manholes,  or 
infiltering  through  the  joints  or  other  defective  places. 
Unless  the  velocity  of  flow  is  sufficient  to  carry  this  matter 
along  it  will  form  deposits  in  the  sewer-invert  which  must  be 
in  some  way  removed. 

There  is  another  class  of  deposits,  composed  of  mycelial 
matter,  which  forms  in  most  house-sewers.  This  contracts 
the  area  of  cross-section  and  may  become  the  breeding-place 
of  micro-organisms;  but  emits  little  odor  and  is  readily  de- 
tached  and  carried  away  by  a  strong  flush  of  water. 


FLUSHING   AND    VENTILATION.  8/ 

To  prevent  these  deposits  the  only  practicable  way  known 
is  to  keep  all  sewers  constantly  flowing  with  a  depth  at  least 
£  the  radius  of  the  invert,  water  being  introduced  for  this 
purpose  if  necessary,  and  also  to  maintain  a  velocity  of  at 
least  i£  feet  per  second.  To  remove  them  the  methods 
employed  are  either  to  occasionally  turn  through  the  sewer 
streams  of  water  of  sufficient  quantity  and  velocity  to  dislodge 
and  remove  the  deposits,  or  to  employ  shovels,  hoes, 
"  pills,"  scrapers,  or  similar  appliances  to  be  described  in 
Chapter  XV. 

The  method  of  prevention,  if  applied  near  a  dead  end, 
where  the  sewage  flow  is  minimum  in  quantity,  even  in  the 
case  of  a  sewer  laid  at  minimum  grade,  would  require  about 
47,000  gallons  per  day  for  each  line  of  6-inch  pipe  and  83,000 
gallons  for  each  8-inch  line.  These  quantities  it  will  usually 
be  impracticable  to  supply;  and  were  it  practicable  the  addi- 
tion to  the  sewage  of  this  amount  in  each  of  several  branches 
would  compel  a  large  increase  in  the  size  of  the  sewer-mains, 
and  greatly  increase  the  cost  of  treatment  in  case  this  method 
of  disposal  was  employed.  There  will  occasionally  be  in- 
stances, however,  where  a  convenient  stream  of  water  can 
be  utilized  to  advantage  in  this  way. 

It  sometimes  happens  that  an  old  sewer-main  or  other 
large  drainage-channel  is  at  so  flat  a  grade  as  to  be,  in  part  at 
least,  a  sewer  of  deposit.  Flushing  can  be  used  to  advantage 
in  such  a  case  to  stir  up  and  remove  the  matter  deposited. 
A  notable  instance  of  this  may  be  found  at  Milwaukee,  Wis., 
where  40,000  gallons  of  lake-water  per  minute  are  pumped 
into  the  Milwaukee  River  (the  flow  of  which  is  largely  sewage) 
for  flushing  it. 

In  general  a  sewer  in  which  there  is  a  continuous  flow 
with  a  depth  of  at  least  J  the  radius  of  the  invert  and  a 
velocity  exceeding  2  feet  will  need  but  infrequent  cleaning  if 
legitimate  sewage  only  be  admitted.  If  for  any  reason  or  at 


88  SEWERAGE. 

any  time  these  conditions  be  not  fulfilled  artificial  cleaning 
will  probably  need  to  be  resorted  to. 


ART.  26.     METHODS  OF  FLUSHING. 

As  stated,  there  are  two  general  methods  of  cleaning 
sewers:  flushing,  and  by  the  use  of  some  kind  of  scraper  or 
similar  tool.  The  latter  usually  calls  for  no  special  provisions 
in  the  construction  and  will  be  treated  of  in  Part  III. 
Flushing,  however,  is  frequently  accomplished  by  appliances 
built  into  the  system,  and  the  principles  involved  are  other 
than  those  controlling  hand  labor;  it  is  therefore  necessary  to 
consider  it  in  designing.  Flushing  may  be  done  by  hand,  by 
automatic  appliances,  or  by  use  of  rain-water. 

By  the  first  the  sewer  can  be  flushed  from  any  manhole, 
as  well  as  from  flush-tanks;  by  the  second  from  fixed  points 
only,  usually  the  heads  of  laterals;  by  the  third  the  flushing- 
water  enters  from  roofs  through  all  or  many  house-connec- 
tions, or  in  some  instances  the  inlets  are  so  constructed  as  to 
store  the  rain-water  from  the  street-surfaces  or  from  water- 
courses and  flush  with  periodic  discharges  of  the  same. 

The  secret  of  successful  flushing  lies  in  compelling  a  large 
mass  of  water  to  move  at  considerable  speed  down  the  sewer. 
If  the  sewer  be  less  than  24  inches  or  30  inches  in  diameter 
water  should  as  far  as  possible  completely  fill  it,  that  deposits 
may  be  removed  from  its  entire  circumference  and  also  that 
the  effect  of  the  flush  may  be  felt  far  down  the  sewer.  With 
the  sewer  flowing  full  bore  at  the  upper  end  the  depth  of  the 
water  will  decrease  as  the  flushing-wave  progresses  down  the 
sewer,  until  at  some  point  below,  at  a  distance  varying  with 
the  size  and  grade  of  the  sewer,  with  the  head  of  water  at  the 
upper  end  and  the  volume  of  sewage  flowing,  the  depth  and 
velocity  of  the  sewage  will  be  but  little  affected  by  the  flush. 

The  initial  velocity  will  depend  upon  the  head  and  upon 


FLUSHING   AND    VENTILATION.  89 

• 

the  facility  offered  the  water  for  entering  the  sewer.  There 
should  be  a  free  and  open  orifice  at  the  entrance  end,  and  if 
possible  the  angle  between  the  inside  of  the  sewer  and  that 
of  the  manhole  or  flush-tank  should  be  rounded.  Speed  is  of 
as  much  value  in  flushing  as  quantity,  and  with  a  given 
amount  of  flushing-water  the  more  quickly  it  can  be  made  to 
pass  through  the  sewer  the  better.  In  most  cases  little 
if  any  benefit  would  result  should  a  faucet  be  left  con- 
tinuously running  in  each  house  in  a  city,  but  y^Vrr  °f  the 
same  amount  of  water  used  in  a  proper  way  would  be  of  great 
benefit  to  the  system. 

Although  for  creating  velocity  the  head  in  the  flush-tank 
should  generally  be  as  great  as  possible,  it  must  be  limited  by 
the  amount  of  internal  pressure  which  the  sewer  can  stand 
without  rupture.  A  few  years  ago  a  brick  sewer  in  Washing- 
ton, D.  C.,  was,  on  account  of  insufficient  size,  put  under 
such  a  head  of  water  by  the  run-off  from  a  cloudburst  that 
its  upper  half  was  completely  severed  from  the  lower  and  the 
sewer  destroyed,  and  a  similar  result  might  follow  from  too 
great  pressure  of  flushing-water.  With  a  pipe  sewer  this 
danger  is  not  so  great.  A  head  of  6  or  8  feet  at  the  manhole 
or  flush-tank — which  is  more  than  can  usually  be  obtained — 
should  not  endanger  a  pipe  sewer.  Brick  sewers  as  ordinarily 
constructed  should  not  be  filled  to  a  point  more  than  5  feet 
above  the  invert  or,  for  those  more  than  5  feet  in  diameter, 
higher  than  the  crown.  In  no  case  should  the  water  be 
backed  up  a  sewer-line  to  such  a  height  as  would  flood  any 
connected  cellars. 

The  flushing-water  should  move  down  and  not  up  the 
sewer,  since  the  effect  of  the  latter  would  probably  be  to 
sweep  the  intermediate  deposits  nearly  to  the  upper  limit  of 
the  wave  and  leave  them  there  to  dam  the  flow.  The  inter- 
val which  should  elapse  between  flushings  will  vary  under 
different  conditions.  In  sewers  where  there  is  a  constant 


QO  SEWERAGE. 

ample  flow  of  water,  where  stoppages  are  few  and  due  solely 
to  accident  or  design  of  ignorant  or  malicious  persons,  flushing 
need  be  resorted  to  only  when  such  stoppages  occur.  If  it  is 
found  from  experience  that  stoppages  are  frequent  or  that 
there  is  a  constant  depositing  of  material  in  the  sewers,  or  if 
it  is  foreseen  that  this  will  occur  from  causes  mentioned  in 
the  previous  article,  frequent  flushings  should  be  provided  for. 

In  the  case  of  a  dead  end  of  a  house  or  combined  sewer, 
or  one  which  has  but  few  house-connections  made  with  it,  the 
flushing  should  be  done  once  in  each  24  or  at  least  48  hours. 

Both  separate  and  combined  systems  have  been  built  and 
satisfactorily  maintained  without  flushing  at  any  point  oftener 
than  two  or  three  times  a  year.  It  is  probable  that  this  is 
possible  only  where  there  is  considerable  ground-water  enter- 
ing the  sewers  at  their  upper  ends,  or  where  the  dead  ends 
occur  only  in  thickly  populated  districts  and  on  grades  a 
little  greater  than  the  minimum  herein  advocated.  There  is 
too  little  definite  information  on  this  subject  to  justify  a  posi- 
tive statement  as  to  when,  if  ever,  flushing  at  dead  ends  may 
be  profitably  omitted.  It  is  advisable  so  to  arrange  every 
house  or  combined  sewer,  where  the  conditions  will  be  those 
given  as  favoring  deposits,  that  it  can  be  satisfactorily  flushed. 

A  few  experiments  have  been  made  on  the  actual  effect 
of  flushing-water  in  a  sewer,  chiefly  with  reference  to  the 
velocity  and  depth  of  the  flushing-water  at  different  distances 
from  the  point  of  entering.  Andrew  Rosewater  found  by 
experiment  with  a  4OO-gallon  tank  at  the  head  of  an  8-inch 
line  of  sewer  discharging  1 1  gallons  per  second  that  at  the 
first  manhole,  200  feet  below  the  flush-tank,  the  water  was 
6  inches  deep  and  had  a  velocity  of  5.6  feet  per  second;  200 
feet  further  the  depth  was  5  inches,  velocity  2.8  feet;  and 
400  feet  further  the  depth  was  4  inches,  velocity  2  feet — 
showing  the  flushing  effect  to  be  practically  exhausted  in  800 
feet.  Mr.  Ogden,  in  experiments  made  in  Ithaca,  N.  Y., 


FLUSHING   AND     VENTILATION.  9! 

in  1897,  found  that  with  discharges  from  flush-tanks  through 
8-inch  pipes  of  from  .89  to  i.i  cubic  feet  per  second  the  flow 
was  reduced  to  2  inches  at  1123  feet  from  the  flush-tank  in 
two  cases  where  the  grades  varied  from  .52$  to  1.31$,  at 
about  1000  feet  in  another  where  the  grades  varied  from 
1.02$  to  3.14$,  and  in  another  where  the  grades  varied  from 
.80$  to  .89$  the  depth  was  4  inches  at  895  feet  from  the 
flush-tank.  In  the  first  two  the  sewer  was  scoured  clean  for 
529  feet  and  some  effect  felt  at  819  feet;  in  the  third  the 
sewer  was  cleaned  for  556  feet  and  the  effect  slight  at  970 
feet;  in  the  last  the  pipe  was  "  disturbed,  but  not  cleaned," 
at  636  feet,  until  600  gallons  were  discharged,  when  it  was 
cleaned  for  more  than  636  feet,  but  less  than  900  feet.  The 
other  discharges  referred  to  were  of  300  gallons  each.  An 
interesting  series  of  experiments  were  conducted  and  their 
results  plotted  by  S.  H.  Adams  in  England.  These  appeared 
to  show,  as  do  the  above,  that  300  gallons  is  in  some  cases 
insufficient  to  properly  flush  an  8-inch  pipe;  also  that  the 
effect  of  such  a  quantity  is  felt  for  about  800  to  1000  feet.* 

In  flushing  by  hand  the  sewer  is  usually  stopped  at  the 
down-grade  side  of  a  manhole  or  flush-tank,  this  is  filled  to  a 
desired  height  with  water  or  by  allowing  the  sewage  to 
accumulate  in  and  above  it,  the  gate,  plug,  or  other  stopper 
is  removed  and  the  water  allowed  to  enter  the  sewer  under 
the  head  due  to  its  height.  Where  outside  water  is  used  for 
flushing  and  is  limited  in  quantity  another  stopper  should  be 
placed  at  the  upper  orifice  in  manholes,  to  prevent  a  flow  up 
the  sewer,  and  left  in  until  the  flushing  is  over.  The  stoppers 
are  made  of  various  forms  and  to  act  in  various  ways,  and  to 
close  the  whole  or  only  the  lower  half  or  two  thirds  of  the 
sewer.  The  water  is  obtained  from  different  sources  and 
introduced  by  different  methods,  a  further  discussion  of  which 
will  be  given  in  Part  III. 

In  England  the  separate  system,  when  first  constructed, 

*  See  also  Transactions  Am.  Soc.  C.  E.,  vol.  XL,  pp.  1-30. 


$2  SEWERAGE, 

was  designed  to  admit  to  the  house-sewers  roof-water  and 
drainage  from  yards,  and  this  method  is  still  followed  there 
to  a  considerable  extent.  In  the  United  States  the  majority 
of  separate  systems  are  not  supposed  to  receive  this  water. 
It  is  argued  by  advocates  of  the  former  practice  that  the 
householder  should  not  be  required  to  construct  two  connec- 
tions, one  for  house-sewage  and  one  for  rain-water.  But  the 
last  can  be  conveniently  discharged  into  the  gutter,  except 
in  the  case  of  buildings  covering  a  large  area,  when  the  cost 
of  the  extra  drain  would  be  relatively  inappreciable. 

Another  argument  for  the  admission  of  roof-water  is  that 
it  is  beneficial  in  flushing  the  sewer.  If  it  is  admitted  only 
.at  and  near  the  dead  ends  it  will  usually  be  advantageous,  but 
it  should  not  be  thought  to  take  the  place  of  all  other  flush- 
ing. The  sewers  are  most  likely  to  need  flushing  at  dry 
seasons,  and  this  must  then  be  done  by  hand  or  otherwise. 
There  is  a  danger  that  the  presence  of  these  roof-connections 
will  give  a  false  idea  that  the  flushing  requirements  have  been 
entirely  met. 

If  roof-water  is  admitted  to  small  sewers  throughout  their 
length  there  is  great  probability  of  its  gorging  the  pipes  and 
backing  up  into  connected  basements  and  cellars.  In  Mount 
Vernon,  N.  Y.,  in  1892  great  damage  was  caused  in  this  way 
and  all  roof-drains  were  at  once  disconnected ;  and  many 
similar  instances  might  be  cited. 

Since  the  danger  is  so  imminent  and  the  benefits  con- 
tributed at  such  uncertain  intervals,  most  American  engineers 
do  not  advise  the  admission  of  roof-water  to  small  sewers. 

Sewers  are  sometimes  flushed  by  connecting  their  upper 
ends  with  convenient  streams,  or  artificial  channels  filled  from 
such  streams,  the  water  being  admitted  periodically  by  gates: 
as  at  Bern,  Wurzburg,  Innsbriick,  Freiburg,  Breslau,  Munich, 
and  other  cities  of  Europe;  also  at  Newton,  Mass. 

Reservoirs  fed  by  streams  or  springs  are  used  in  Munich, 


FLUSHING   AND    VENTILATION.  93 

Cologne,  Wiesbaden,  Frankfurt,  Stuttgart,  and  other  cities. 
At  the  first-mentioned  place  large  underground  reservoirs,  one 
of  which  is  6  feet  6  inches  by  4  feet  7  inches  and  extends  along 
two  blocks,  are  filled  from  the  Isar  River. 

Tides  are  sometimes  made  use  of  for  this  purpose,  the 
water  being  allowed  to  rise  in  the  sewer  at  high  tide  and 
being  held  there  by  gates  until  the  low  tide,  when  it  is 
released.  Ordinarily  only  the  lower  reach  of  the  outlet  sewer 
can  be  thus  flushed.  A  better  method  in  some  cases  is  to 
hold  the  water  after  high  tide  in  a  basin  from  which  it  is 
rapidly  discharged  at  low  tide  into  the  sewers  to  be  flushed. 

As  in  the  case  of  Milwaukee,  already  cited,  and  of  Bre- 
men, the  flushing-water  may  be  pumped  from  a  lake  or  river 
directly  to  the  sewer.  This  is  of  course  applicable  within  the 
limits  of  economy  to  very  large  sewers  only,  or  to  a  system- 
where  a  number  of  dead  ends  can  be  reached  by  a  compara- 
tively short  line  of  water  pipe. 

The  water  for  flushing  is  sometimes  taken  from  the  ocean 
or  other  body  of  salt  water;  but  the  salts  are  thought  to 
decompose  the  sewage,  giving  rise  to  gases  and  deposits  of 
matter  rendered  insoluble,  and  are  corroding  to  any  metal- 
work  in  the  sewers.  Hence  its  use  is  not  advised  by  most 
authorities. 

ART.  27.     APPLIANCES  FOR  FLUSHING. 

Automatic  flush-tanks  are  in  use  in  a  large  number  of  sep- 
arate systems,  but  are  seldom  used  for  flushing  combined  or 
storm-water  sewers,  owing  to  the  enormous  quantities  of 
water  needed  for  that  purpose.  There  have  been  a  great 
number  of  devices  invented  for  flushing.  Most  of  those  at 
present  used  in  any  considerable  numbers  are  siphons  in  prin- 
ciple, so  arranged  that  a  tank  in  which  they  are  set  may  fill 
gradually  up  to  a  certain  point,  when  its  contents  are  dis- 


94  SEWERAGE. 

charged  rapidly  into  the  sewer.  The  tanks  are  made  to  con- 
tain at  the  time  of  discharge  from  150  to  600  or  even  1200 
gallons  for  6-  to  lO-inch  pipe  sewers.  For  larger  sewers  larger 
quantities  are  provided.  The  smaller  quantities  are  of  little 
use.  No  tank  should  discharge  less  than  250  gallons  at  a  time 
into  a  6-inch  pipe,  and  correspondingly  larger  amounts  into 
larger  sewers.  500  to  800  gallons  discharged  into  an  8-inch 
pipe  once  in  24  hours  would  be  more  beneficial  than  half  of 
that  amount  at  each  of  three  or  four  discharges  during  the 
same  time.  It  is  probable,  however,  that  in  sewers  calculated 
for  a  velocity  exceeding  5  feet  per  second  equal  efficiency  may 
be  obtained  with  quantities  less  than  those  stated. 

The  tanks  should,  of  course,  be  water-tight.  They  are 
usually  built  of  brick  plastered  on  both  the  inside  and  the  out, 
but  might  be  made  of  wood  or  of  iron.  They  should  be  so 
built  and  arranged  that  the  water  may  have  the  greatest  per- 
missible head  above  the  sewer  when  discharging.  (For  details 
see  Art.  47.) 

The  water  may  be  conveniently  admitted  to  the  tank 
through  a  half-inch  or  smaller  stop-cock  connected  with  the 
street-main  by  a  supply-pipe  passing  through  the  tank-wall. 
This  cock  is  continually  left  sufficiently  open  to  cause  the 
tank  to  fill  and  discharge  at  desired  intervals.  If  the  water  is 
inclined  to  be  muddy  at  times  the  use  of  too  large  a  supply- 
pipe  will  result  in  the  choking  of  it  by  sedimentation.  It 
should  be  of  such  a  size  that  the  quantity  to  be  used  in  the 
tank  will  pass  through  it  with  a  velocity  of  2  feet  per  second 
or  more. 

The  discharge-pipe  of  the  tank  should  be  at  least  as  large 
as  the  sewer.  It  would  be  better  to  have  it  a  size  or  two 
larger  and  bell-mouthed  at  the  end,  but  this  is  seldom 
done. 

The  automatic  flushing  appliances  most  in  use  in  the 
United  States  are  further  referred  to  in  Chapter  VIII.  They 


f LUSH  ING   AND    VENTILATION.  95 

are,  most  of  them,  covered  by  patent,  and  the  prices  range 
upward  from  about  $12  for  a  tank  to  discharge  150  gallons 
through  a  5 -inch  pipe. 

Where  automatic  flush-tanks  are  not  used  some  engineers 
have  built  into  manholes  at  dead  ends  2-inch  to  4-inch  pipes 
connected  with  adjacent  water-mains  and  provided  with  gate- 
valves,  as  at  Mount  Vernon,  N.  Y.,  and  Newton,  Mass. 
This  is  probably  the  most  convenient  method  of  hand-flushing 
and  the  cheapest  to  operate.  The  cost  at  Mount  Vernon  was 
about  $40  for  each  4-inch  branch  and  connection. 

There  are  numerous  methods  of  flushing  by  hose,  by 
water-tanks,  etc.,  many  of  which  are  described  in  Part  III. 

In  flushing  by  rain-water  no  special  appliances  are  ordi- 
narily used,  the  roofs  and  sometimes  the  yards  being  con- 
nected in  the  ordinary  way  with  the  sewer. 

Special  methods  involving  pumping,  some  instances  of 
which  have  been  referred  to,  need  no  description,  since  the 
details  will  vary  with  each  case. 

ART.  28.     NECESSITY  FOR  VENTILATION. 

In  every  sewer  there  is  a  space  above  the  sewage  filled 
with  air,  and  this  air,  it  is  evident,  will  generally  be  far  from 
pure  unless  kept  in  motion  and  frequently  renewed.  The 
odor  accompanying  all  sewage,  even  when  there  is  no  decom- 
position proceeding  in  the  sewer,  is  communicated  to  this  air; 
there  will  frequently  be  given  off  some  gases  due  to  putrefac- 
tion; and  it  is  possible  that  malefic  germs  may  escape  in 
vapor  from  the  sewage  or  from  deposits  in  the  sewer,  to  be 
carried  along  by  the  air-currents.  This  air  probably  is  seldom 
motionless.  It  is  influenced  by  the  sewage  to  move  down  the 
sewer;  it  is  warmer  in  winter  and  often  in  summer  than  the 
outside  air,  which  condition  occasions  motion  when  there  is 
communication  between  the  two;  it  is  driven  out  of  or  along 


g6  SEWERAGE. 

the  sewer  by  sudden  inflows  of  sewage  from  house-connections 
or  branches  and  sucked  in  by  decrease  in  the  volume  of  flow; 
near  the  outlet  the  direction  and  force  of  the  wind  affect  it, 
driving  it  up  the  sewer  or  sucking  it  out;  last,  and  most  im- 
portant, it  passes  into  empty  or  partly  empty  house-connec- 
tions and  into  proximity  to,  if  not  into  the  air  of,  connected 
residences.  Herein  lies  the  danger.  There  is  no  "  sewer- 
gas  "  which  is  deadly  to  human  life,  but  it  is  known  that  air 
which  has  been  confined  in  contact  with  decomposing  sewage 
is  charged  with  "  an  ever- varying  mixture  of  gases;  and  of 
those  that  are  deleterious  the  more  prominent  are  sulphuretted 
hydrogen,  sulphide  of  ammonium,  and  caburetted  hydrogen; 
while  ammonia,  carbonic  acid,  and  occasionally  carbonic  oxide 
derived  from  leakage  of  illuminating-gas  into  sewers  are 
present  in  more  or  less  large  proportions."  (W.  P.  Gerhard, 
"  Sanitary  House  Inspection.") 

The  least  that  can  be  said  of  these  is  that  they  lessen  the 
vitality  and  prepare  the  way  for  easy  conquest  by  diseases 
that  might  otherwise  obtain  no  hold  upon  the  system ;  they 
should  therefore  be  excluded  from  all  occupied  buildings. 
The  danger  due  to  impure  air  in  dwellings  has  led  the  New 
York  Board  of  Health  to  conclude  that  "  40%  of  all  deaths  are 
caused  by  breathing  impure  air."  Playfair  asserts  that  in 
modern  hygiene  "  nothing  is  more  conclusively  shown  than 
the  fact  that  vitiated  atmospheres  are  the  most  fruitful  sources 
of  disease."  Death  rates  have  been  "  reduced  in  children's 
hospitals  from  50$  to  5$  by  improved  ventilation." 

While  the  vitiation  referred  to  in  these  quotations  is  not 
that  of  sewer-air  exclusively,  this  is  included  among  the 
causes  of  it  and  produces  the  same  effect.  Unfortunately  the 
most  numerous  and  fruitful  sources  of  the  gases  are  found, 
not  in  the  sewer,  but  in  the  house-connections  or  soil-pipes, 
and  consequently  not  directly  under  the  control  of  the 
authorities.  The  methods  necessary  to  prevent  danger  from 


FLUSHING  AND    VENTILATION.  97 

these  sources  will  be  considered  under  the  head  of  House- 
connections  (Art.  82). 

ART.  29.     METHODS  OF  VENTILATION. 

It  is  evident  that  the  danger  from  sewer-air  may  be 
avoided,  or  at  least  lessened,  in  two  ways:  by  preventing  the 
creation  of  gases,  and  by  preventing  the  sewer-air  from  reach- 
ing human  beings  in  dangerous  quantities  or  under  dangerous 
conditions.  No  method  has  yet  been  found  for  perfectly 
accomplishing  either  of  these  aims  in  practice,  but  both  may 
be  partially  attained. 

Aside  from  illuminating-gas  most  of  the  objectionable 
gases  are  given  off  by  putrefaction,  and  the  prevention  of  this 
in  the  sewers  is  therefore  most  necessary.  This  is  best 
accomplished  by  the  removal  of  all  sewage  to  the  outlet  before 
putrefaction  can  begin ;  and  here  is  seen  the  advantage  of 
daily  flushing,  cleaning  the  upper  laterals  of  deposits  before 
they  reach  this  dangerous  stage.  The  use  of  disinfectants  in 
sewage  for  this  purpose  is  seldom  advisable,  both  on  account 
of  the  enormous  cost  and  practical  difficulties  of  applying 
them  and  because  the  various  and  changing  characters  of 
sewage  in  different  cities  and  from  hour  to  hour  may  intro- 
duce such  matter  as  will  combine  with  any  given  disinfectant 
to  produce  deposits  and  gases  fully  as  injurious  as  those  due 
to  sewage  alone.  The  transporting  of  germs  by  sewer-air  is 
probably  reduced  by  reducing  putrefaction,  although  there  is 
very  little  definitely  known  on  this  point,  it  being  uncertain 
even  whether  disease-germs  are  carried  by  sewer-air  at  all. 

To  prevent  air  from  the  sewer  from  entering  houses  two 
general  methods  are  in  use:  placing  a  barrier  in  the  house- 
connection,  and  removing  the  sewer-air  through  other  outlets. 
The  former  is  one  of  the  aims  of  the  plumber  and  is  usually 
attempted  by  the  use  of  traps.  The  latter  has  been  aimed  at 


98  SE  WERA  GE. 

by  the  use  of  many  ventilating  devices,  in  few  or  none  of 
which  has  positive  action  been  successfully  obtained.  A 
combination  of  these  two  methods  gives  reasonably  good 
results  in  most  cases,  a  partial  obstruction  to  the  air  being 
placed  in  the  house-connection  or  its  branches  in  the  shape 
of  water-sealed  traps,  and  the  power  of  the  air  to  force  its 
way  through  these  being  lessened  by  ventilation. 

If  the  sewer  were  a  tight  conduit  with  no  inlets  or  outlets 
except  through  the  house-connections  and  the  main  outlet 
the  sewer-air  must  remain  constantly  unchanged  and  stagnant, 
or  must  find  exit  and  entrance  through  these  house-connec- 
tions. The  first  condition  is  impossible,  for  the  amount  of 
sewage  varies  from  hour  to  hour  and  must  displace  and  in  turn 
be  displaced  by  air  driven  to  and  derived  from  some  outside 
source.  In  case  of  a  sudden  discharge  of  sewage  into  such  a 
sewer  the  air  will  be  driven  through  the  only  outlets — the 
house-connections — unsealing  the  main  traps,  and  the  second- 
ary ones  also  unless  these  be  amply  vented.  A  strong  wind 
blowing  up  the  sewer  from  the  outlet  may  produce  the  same 
result.  In  addition  to  other  ventilation  of  both  sewer  and 
soil-pipe  it  is  therefore  advisable  to  thoroughly  vent  all  house- 
traps. 

Attempts  have  been  made  to  constantly  remove  the  air 
from*  sewers  by  either  sucking  out  the  foul  air  or  forcing  in 
fresh;  that  is,  by  producing  a  current  through  the  sewer  to  a 
given  outlet  by  either  the  vacuum  or  plenum  process.  Both 
have  proved  failures  as  well  as  very  expensive.  In  no  experi- 
mental case  has  the  effect  been  felt  more  than  1000  feet  from 
the  fans  or  other  apparatus,  not  only  on  account  of  the  great 
amount  of  air  in  the  sewer-mains  and  laterals  to  be  moved, 
but  because  the  traps  in  the  house-connections  were  unsealed 
by  the  pressure  and  air  admitted  from  or  forced  into  the 
buildings,  according  to  the  system  employed. 

The  Metropolitan  Board  of  Works,  London,   concluded, 


TNlVERSITY 


FLUSHING   AND    VENTILATION.  99 

after  exhaustive  study  of  the  question,  "  that  the  method  of 
ventilation  adopted  in  mines,  where  there  are  only  two  open- 
ings to  be  dealt  with  (an  inlet  for  the  air  at  one  end  and  an 
outlet  for  it  at  the  other),  is  inapplicable  to  sewers."  This 
characteristic  of  a  sewerage  system  renders  impracticable  all 
methods  of  ventilation  depending  upon  one  or  two  ventilators 
to  each  line  of  sewers:  such  as  connecting  the  sewer-end  with 
a  chimney,  which  would  afford  little  more  ventilation  than  an 
untrapped  soil-pipe  at  the  same  point  or  a  special  ventilating- 
manhole. 

Many  expedients  for  ventilation  have  been  devised  and 
tried  —  among  them  connecting  the  sewers  to  street-lamps, 
where  a  suction  is  caused  and  the  gas  burned  by  a  constant 
flame;  placing  in  the  crown  of  brick  sewers  small  perforated 
pipes  connected  with  "  uptake-shafts,"  expected  to  cause  a 
continuous  removal  of  the  gases;  leading  pipes  from  the 
sewer  to  special  flues  constructed  in  houses,  within  the  body 
of  the  walls,  adjacent  to  the  chimney,  or  upon  the  outside  of 
the  house  and  running  up  above  all  windows;  leaving  the 
main  house-drains  untrapped  and  extending  them  above  the 
roofs;  placing  flap-doors  in  the  sewers,  opening  downward  for 
the  sewage,  but  closed  to  air,  which  can  escape  through  open- 
ings just  above  such  flaps;  placing  in  the  street  centre  at 
intervals  along  the  sewer  manholes  or  other  ventilating-shafts 
with  perforated  covers;  connecting  the  sewers  by  untrapped 
pipes  with  street-inlets  at  the  curb  line.  In  connection  with 
these  charcoal  and  other  deodorizers  are  sometimes  placed  at 
the  air-outlets.  (See  "  General  Conclusions,  Metropolitan 
Board  of  Works,"  London.) 

There  seems  to  be  evidence  in  favor  of  the  conclusion  that 
the  greatest  danger  exists  in  the  house-connections  themselves 
and  not  in  the  sewers,  although  the  latter  should  be  prevented 
from  contributing  to  this  danger.  Of  many  analyses  of  sewer- 
air  made  not  one  to  the  author's  knowledge  has  shown  a 


I OO  SE  WERA  GE. 

greater  impurity  than  that  in  a  crowded  city  street,  whether 
CO,,  oxygen,  or  bacteria  be  taken  as  the  basis  of  comparison. 
Equally  positive  proof  goes  to  show  that  the  average  house- 
connection  or  the  adjacent  soil  near  open  joints  in  the  same 
does  give  rise  to  dangerous  gases.  (It  is  probable  that  the 
upper  ends  of  branch  sewers,  if  not  flushed  well  and  often,  are 
open  to  the  same  charge.)  However,  a  rush  of  comparatively 
pure  air  from  the  sewer  forced  through  the  traps  of  a  foul 
house-connection  is  as  objectionable  as  though  it  itself  were 
polluted,  since  it  forces  into  the  building  the  impure  air  exist- 
ing in  such  connection.  The  vents  on  all  traps  should  hence 
be  of  such  capacity  and  so  placed  as  to  give  full  and  imme- 
diate passage  to  all  the  air  necessary  to  prevent  forcing  or 
siphoning  of  traps. 

This  fact,  that  the  house-connections  themselves  are  fully 
as  foul  as,  if  not  more  so  than,  the  sewers  should  be  more 
generally  recognized  and  better  provision  made  for  ventilating 
them.  This  is  reasonably  well  done  by  placing  a  vent-shaft 
just  above  the  main  trap,  continuing  the  soil-pipe  above  the 
roof  and  venting  each  trap  throughout  the  house.  But  a  still 
better  circulation  of  air  is  obtained  by  omitting  the  main  trap 
altogether  and  permitting  the  air  from  the  sewer  to  pass 
through  the  house-connection  unobstructed.  The  danger  of 
this  air  passing  the  traps  on  house-fixtures  is  no  greater  than 
that  of  the  soil-pipe  air  doing  the  same,  and  in  the  majority 
of  cases  the  sewer  air  is  the  less  dangerous.  Such  construc- 
tion is  also  of  great  assistance  in  ventilating  the  sewer.  If 
only  an  occasional  house-connection  be  left  untrapped,  how- 
ever, the  odors  from  this  may  be  objectionable,  the  sewer  air 
being  but  little  diluted  by  the  infrequent  openings.  But  the 
author  knows  of  no  city  which  makes  this  method  compul- 
sory in  all  connections  where  it  is  not  perfectly  satisfactory. 
(See  also  page  344.) 


FLUSHING   AND    VENTILATION.  IOI 

The  use  of  street-lamps  as  outlets  may  be  advantageous,  but 
the  electric  light  has  rendered  argument  for  and  against  this  plan 
obsolete.  The  use  of  hollow  electric-light  poles  has  recently 
been  introduced  in  Columbus,  O.,  with  what  success  it  is  too 
early  yet  (1899)  to  state.  The  use  of  flap-doors  in  the  sewers 
presupposes  a  regular  flow  of  air  in  a  fixed  direction  through  the 
sewer,  which  investigation  has  found  does  not  ordinarily  exist; 
this,  however,  may  be  advantageous  on  steep  grades,  where 
there  is  a  tendency  for  the  air  to  rise  past  intermediate  venti- 
lating-points  to  the  highest  ones.  Ventilation  through  man- 
holes and  other  ventilating-shafts  most,  if  not  all,  engineers 
recommend,  although  many  do  not  consider  these  sufficient. 

The  use  of  storm-water  inlets  for  this  purpose  is  much 
opposed  by  many,  who  contend  that  the  sewer-air  should  not 
be  discharged  so  near  to  passers-by  upon  the  sidewalk.  In 
fact  this  same  argument  is  used  by  a  few  against  ventilation 
through  manholes  in  the  centre  of  the  street.  It  is  probable 
that  the  danger  from  this  cause  is  very  slight,  if  it  exists  at  all, 
since  it  is  dependent,  not  upon  the  gases,  which  are  enor- 
mously diluted  upon  reaching  the  outer  air,  but  upon  the 
presence  of  disease-germs  in  the  exhalations,  which  is  not 
proven.  Moreover,  the  average  catch-basin,  even  if  just 
cleaned  (as  this  cleaning  is  ordinarily  done),  is  more  offensive 
than  any  rightly  designed  sewer  is  at  all  likely  to  become ;  and 
it  is  extremely  doubtful  if,  in  connection  with  its  odors,  any 
contribution  of  air  from  the  sewer  could  be  detected.  For 
these  reasons  it  seems  to  the  author  desirable  to  connect  the 
sewer  with  the  street-inlets  by  ventilating-pipes  and  to  place 
manholes  with  perforated  heads  at  intervals.  Since  the 
latter  are  apt  to  be  sealed  in  winter  by  ice  and  snow,  and  in 
summer  by  mud,  the  additional  ventilation  through  the  street- 
inlets  would  seem  to  be  advisable,  particularly  if  the  sewer  be 
not  ventilated  through  the  house-drains.  A  small  amount  of 
snow  will  not  ordinarily  stop  the  openings  in  a  manhole-cover, 


102  SEWERAGE. 

owing  to  the  warm  air  of  the  sewer,  but  a  heavy  storm  or 
frozen  mud  may  easily  do  so. 

Since  the  proportion  of  air  in  a  small  sewer  to  the  dis- 
charge into  the  same  is  much  less  than  in  the  case  of  a  large 
combined  sewer,  and  consequently  the  effect  of  a  given  dis- 
charge is  a  greater  compression  of,  and  pressure  transmitted 
by,  the  air  in  the  smaller  sewer,  the  sewers  of  the  separate 
system  need  ventilation  or  safety-vents  even  more  than  do 
those  of  the  combined.  In  case  there  are  storm-water  inlets 
to  which  ventilation-pipes  from  house-sewers  may  be  led  this 
method  may  be  adopted ;  but  ventilation  through  untrapped 
house-connections  is  probably  more  efficient.  This  extra 
ventilation  is  very  often — perhaps  in  the  majority  of  cases — 
neglected,  but  such  omission  is  undoubtedly  attended  with 
danger. 

For  house-sewers,  ventilating  manhole-heads  and  un- 
trapped house-drains;  for  combined  sewers,  these  with  the 
addition  of  untrapped  street-inlets;  and  for  storm-sewers, 
manholes  and  inlets — these,  with  flap-doors  on  steep  grades, 
seem  to  the  author  the  best  methods  so  far  devised  for  ven- 
tilation ;  and  without  ventilation  any  system  will  almost  surely 
become  a  nuisance  and  a  danger.  The  aim  should  be  to  se- 
cure by  whatever  method  the  greatest  possible  number  and 
freedom  of  communications  between  the  sewer  and  the  outer 
air;  and  there  is  little  doubt  but  that  when  this  is  realized 
the  sewer  air  becomes  so  diluted  and  the  organic  matter  float- 
ing in  it  so  oxidized  as  to  render  it  less  dangerous  and  objec- 
tionable than  the  air  of  a  crowded  church  or  theatre.  When 
this  is  not  true  the  sewers  are  probably  in  great  need  of  clean- 
ing and  flushing. 


CHAPTER   VI. 
COLLECTING  THE   DATA. 

ART.  30.     DATA  REQUIRED. 

ANY  plans  made  before  the  full  and  complete  data  are  at 
hand  may  be  shown  by  further  information  to  be  inadvisable, 
while  their  very  existence  may  create  a  prejudice  against  the 
substitution  of  more  efficacious  ones.  Therefore,  although 
the  development  of  the  plans  may  suggest  the  desirability  of 
further  data  the  necessity  for  which  was  unforeseen,  as  much 
as  seems  necessary  in  this  line  and  that  of  surveys  should  be 
done  preliminary  to  any  designing. 

The  first  necessity  will  be  for  a  map  of  the  district  under 
consideration.  This  will  usually  include  the  city  or  town 
and  all  land  over  which  it  may  spread  in  the  future ;  also  all 
adjacent  areas  which  shed  their  water  into  or  across  the  sur- 
face of  this  territory.  This  map  should  show  all  streets,  lanes, 
etc. ;  all  parks  or  other  areas  permanently  devoted  to  vegeta- 
tion; all  rivers,  creeks,  ponds,  or  other  bodies  of  water — in 
fact  all  natural  and  artificial  divisions  of  the  area  embraced  by 
the  corporate  limits.  It  usually  happens  that  this  much  can 
be  found  already  mapped  for  other  purposes;  but  unless  it  is 
known  that  the  measurements  from  which  such  map  was  pre- 
pared were  accurately  taken  a  sufficient  number  of  check 
measurements  should  be  made  to  establish  its  accuracy  or  the 
reverse.  On  the  point  of  accuracy  a  question  may  arise  as  to 
how  exactly  the  measurements  should  be  taken.  If  these 

103 


104  SEWERAGE. 

should  involve  an  error  of  no  more  than  .2%  they  would  be 
sufficiently  accurate  for  the  work  in  hand.  For,  as  sewer 
grades  are  ordinarily  run  from  manhole  to  manhole,  and  these 
are  about  300  feet  apart,  an  error  of  .2%  would  mean  that  of 
.6  foot  in  that  distance,  which  on  a  grade  of  .5$  (a  fairly 
steep  one)  would  involve  an  error  in  grade  of  .003  foot,  which 
is  much  less  than  the  least  which  could  be  expected  in  the 
construction  of  the  sewer. 

It  will  be  advisable  to  obtain  also  the  location  of  all  street- 
railroads,  and  of  all  gas-  and  water-pipes,  their  distance  from 
the  curb  or  side  lines  of  the  street  and  the  depth  of  the 
pipes  being  noted.  Also  the  location,  grade,  size,  and  con- 
dition of  any  existing  sewers  and  appurtenances  should  be 
ascertained,  by  actual  inspection  if  possible. 

The  data  for  computing  the  extent  of  tributary  drainage- 
areas  will  ordinarily  need  to  be  collected  in  their  entirety,  as 
it  is  seldom  that  such  information  exists  in  a  serviceable  form. 
The  topographical  surveys  which  have  been  made  of  several 
of  the  States,  however,  may  be  used  to  great  advantage  in 
this  connection.  The  data  desired  includes  the  boundaries 
of  the  watersheds  whose  run-off  does  not  reach  a  confined 
channel  before  entering  the  limits  of  the  territory  to  be 
sewered.  (Such  water  as  passes  through  this  territory  in  the 
form  of  streams  rather  than  flowing  over  the  ground  does  not 
affect  the  problem,  unless  these  streams  are  to  be  walled  in, 
in  which  case  each  one  will  form  a  problem  by  itself.)  Also 
the  slope  of  the  ground  and  the  character  of  the  soil  as  to 
permeability  should  be  ascertained,  the  location  and  extent 
of  rock  at  or  near  the  surface,  of  woods  and  of  orchards. 
Care  should  be  taken  to  note  and  locate  any  slightly  worn 
channels  along  which  storm-water  ordinarily  flows  to  the 
nearest  creek  or  rivulet  across  territory  not  yet  built  up,  as 
these,  if  they  cross  into  the  sewer  district,  indicate  the  points 
at  which  the  storm-water  must  be  intercepted. 


COLLECTING    THE   DATA.  1 05 

Such  levels  must  be  taken  as  are  necessary  for  the  plot- 
ting of  profiles  of  each  street,  alley,  or  any  other  surface  under 
which  a  sewer  is  to  run,  including  a  profile  across  the  bed  of 
each  stream  crossed,  with  the  elevation  of  high-  and  low-water 
marks;  also  the  elevation  of  the  body  of  water  into  which 
either  the  crude  or  purified  sewage  is  to  be  discharged,  the 
elevation  during  drought  and  flood  as  well  as  the  ordinary 
elevation  being  ascertained.  The  depths  must  be  obtained 
of  all  cellars  whose  bottoms  are  not  evidently  above  the  grade 
of  the  proposed  sewer,  unless  all  sewers  are  to  be  placed  at  a 
fixed  minimum  depth,  which  is  to  be  increased  only  by  the 
demands  of  the  necessary  sewer  grades  and  not  by  the  depth 
of  any  cellar  or  basement  (see  Art.  37).  Also  if  grades  have 
been  adopted  for  any  street,  but  not  yet  carried  into  effect, 
these  as  well  as  the  existing  surfaces  should  be  obtained. 

If  a  disposal-ground  is  to  be  used  for  filtration  or  irriga- 
tion a  careful  levelling  of  its  entire  surface  must  be  made, 
and  test-pits  sunk  to  ascertain  the  character  of  the  material 
to  a  depth  of  5  to  8  feet. 

If  it  is  considered  desirable  to  discharge  the  crude  sewage 
into  a  given  body  of  fresh  or  salt  water  careful  search  should 
be  made  for  the  point  best  suited  for  the  outlet;  also  in  case 
of  a  river  whether  the  dilution  afforded  in  time  of  drought 
will  be  sufficient  to  prevent  a  nuisance.  For  this  purpose  the 
action  of  currents,  tides,  and  prevailing  winds  should  be 
investigated.  Gaugings  of  the  discharge  of  streams  should 
be  made,  and  inquiry  as  to  whether  and  at  what  points  further 
down  the  river  the  water  is  used  for  a  public  supply.  It  is 
well  also  to  have  analyses  made  of  river-water  taken  at  inter- 
vals below  the  proposed  outlet  for  use  in  possible  suits  against 
the  city  for  nuisance;  this  whether  or  not  the  sewage  is  to 
be  treated. 

The  engineer  should  in  person  pass  through  every  street 
in  the  district  to  be  sewered,  noting  the  character  of  each,  the 


100  SEWERAGE. 

location  of  the  business  and  factory  districts,  the  general 
character  of  the  pavements  and  yards,  and  the  average  size  of 
lot  occupied  by  each  residence.  He  must  also  ascertain  as 
nearly  as  may  be  the  present  population  and  its  past  rate  of 
increase;  the  probable  direction  and  extent  of  the  future 
growth  of  the  business  part  of  the  city,  as  well  as  of  the  city 
as  a  whole.  He  should  obtain  the  figures,  if  they  exist,  of 
water-consumption  in  this  and  neighboring  cities;  also  all 
possible  data  concerning  the  rainfall. 

A  considerable  amount  of  other  information  will  in  many 
instances  be  desirable,  called  for  by  the  peculiarities  of  each 
case.  Many  items,  such  as  cost  of  materials  and  labor  (for 
use  in  the  estimate),  will  suggest  themselves  as  they  are 
needed. 

ART.  31.     SURVEYING  AND  PLOTTING. 

Since  extreme  accuracy  is  not  necessary  in  the  transit 
survey,  the  use  of  the  ordinary  stadia  methods  will  be  found 
advantageous  for  either  check  or  original  surveys.  Stadia- 
hairs  in  the  level,  for  use  in  running  street-profiles,  will  be 
found  to  expedite  this  work,  and  will  permit  reducing  the 
number  in  the  level  party  to  two.  The  adjustment  of  the 
stadia-hairs  should  be  frequently  checked. 

The  tributary  drainage-areas  will  not  need  to  be  surveyed 
in  great  detail.  If  the  natural  features  are  boldly  accentuated 
it  may  be  sufficient  to  locate  by  a  transit-line  the  limiting 
summits  and  ridges,  both  main  ridges  and  spurs.  If  the 
country  is  gently  rolling  or  generally  flat  contour  surveys 
should  be  made  of  the  whole  drainage-area,  or  at  least  of  any 
portion  of  it  the  disposal  of  whose  run-off  may  offer  difficul- 
ties. 

Of  such  undeveloped  areas  as  may  be  reached  by  the  city 
in  its  future  growth  and  which  will  be  embraced  in  drainage- 
areas  for  which  sewers  are  to  be  at  once  designed  accurate 


COLLECTING    THE  DATA. 

contour  surveys  should  be  made,  contours  being  located  from 
i  to  25  feet  apart  vertically,  according  to  the  nature  of  the 
country.  They  should  be  sufficiently  close  to  show  the  con- 
figuration of  the  ground  in  considerable  detail,  but  not  so  close 
that  the  contour-lines  will  obscure  all  else  upon  the  map. 

Most  cities  and  towns  of  any  size  have  the  street  grades 
established  and  recorded  with  their  profiles.  An  extensive 
experience  in  attempts  at  the  adaptation  of  such  information 
to  the  requirements  of  sewer-designing  has  demonstrated  that 
in  nine  cases  out  of  ten  it  is  waste  of  time  to  attempt  to  use 
these  records  and  profiles.  For  the  levels  have  usually  been 
taken  by  a  succession  of  surveyors  of  varying  degrees  of 
efficiency;  occasionally  also  the  grades  have  been  altered  on 
the  ground,  but  not  upon  the  profile;  and  the  time  employed 
in  discovering  and  rectifying  errors  and  omissions  would 
generally  have  sufficed  for  taking  entirely  new  levels. 

The  levels  of  the  street-surfaces  taken  for  the  profile 
need  be  to  tenths  of  a  foot  only,  but  the  bench-marks  and 
back-  and  fore-sights  should  be  to  thousandths.  Readings 
should  be  taken  along  each  proposed  sewer-line  not  more  than 
100  feet  apart,  at  every  pronounced  change  of  grade  and  at 
street  intersections;  the  elevation  of  rails  where  the  line 
crosses  a  railway,  and  at  stream-crossings  the  profile  of  the 
bottom  and  the  water-surface,  should  be  obtained. 

A  convenient  scale  for  a  map  of  a  village  or  borough  is 
200  feet  to  I  inch,  but  if  its  size  is  such  that  this  scale  would 
necessitate  the  use  of  paper  more  than  3  feet  wide  it  may  be 
better  to  use  a  scale  of  250  or  300  feet  to  I  inch.  It  is  inad- 
visable to  use  a  smaller  scale  than  this,  and  if  the  resulting 
map  is  still  too  large  for  the  paper  it  may  be  necessary  to 
spread  it  over  two  or  more  sheets.  In  such  a  case  it  will  be 
found  convenient,  where  conditions  permit  of  it,  to  so  arrange 
the  sheets  that  each  drainage-area  shall  appear  upon  one  sheet 
only.  Upon  this  map  should  be  shown  the  location  of 


IO8  SEWERAGE. 

the  proposed  sewers  and  all  appurtenances,  these  being 
usually  in  red. 

A  convenient  scale  for  the  profiles  is  25  feet  to  i  inch 
horizontal  and  5  feet  to  I  inch  vertical.  These  should  show 
the  sewer-line  at  its  proper  grade,  the  depth  of  all  unusually 
low  cellars,  the  location  of  all  manholes  and  other  appurte- 
nances. A  plan  of  the  street  is  usually  placed  under  the 
profile,  showing  the  location  therein  of  the  sewer-line  and  all 
appurtenances. 

For  ascertaining  the  best  location  for  an  outlet  into  tidal 
^waters  the  use  of  floats  is  desirable,  since  thus  can  be  learned 
the  ordinary  periodic  movements  of  the  water  into  which  the 
sewage  is  to  be  discharged,  and  hence  the  possibility  of  the 
creation  of  a  nuisance  thereby.  These  floats  should  expose 
as  little  surface  to  the  wind  as  possible.  A  pine  rod  or  tin 
tube,  weighted  at  the  botom  and  with  a  numbered  flag 
fastened  to  the  top,  is  usually  employed.  They  should  be 
started  at  different  stages  of  the  tide  from  each  point  which 
is  being  considered  as  a  possible  outlet.  Account  should  be 
kept  of  and  allowance  made  for  winds  during  the  times  the 
floats  are  in  the  water.  Each  float  should  be  numbered  and 
a  record  kept  showing  the  time  and  place  at  which  it  was  put 
into  the  water,  the  state  of  the  tide,  wind,  etc.  By  means 
of  one  or  more  boats  they  should  be  so  traced  that  the  path 
•of  each  can  be  plotted  upon  a  map  until  it  strands  or  passes 
beyond  the  point  where  sewage  can  create  a  nuisance.  It 
may  at  times  be  necessary  to  follow  a  set  of  floats  night 
.and  day  for  three  or  four  days;  seldom  longer  than  this,  for 
if  they  have  not  in  that  time  passed  to  a  considerable  distance 
from  the  starting-point  such  point  is  not  suitable  for  an 
outlet. 

The  quantity  of  water  flowing  in  a  given  stream  and  the 
resulting  dilution  can  be  ascertained  by  the  use  of  floats  or  a 
current-meter,  the  cross-section  of  the  stream  being  first 


COLLECTING    THE  DATA. 


lOO/ 


obtained.  In  some  cases  this  flow  can  be  obtained  from 
government  or  State  records  of  gaugings.  If  possible  a  gaug- 
ing of  the  stream  during  a  drought  should  be  obtained,  since 
it  is  even  more  important  that  there  be  the  necessary  dilution 
at  such  a  time  than  when  the  river  is  high. 

It  is  sometimes  desirable  to  sink  test-pits  or  bore  at  inter- 
vals along  the  line  of  each  proposed  sewer  to  ascertain  the 
character  of  the  material  to  be  excavated.  This  is  unneces- 
sary where  cellars  or  other  excavations  along  the  street-line 
have  been  sunk  to  practically  the  depth  of  the  sewer,  and 
when  neither  rock  nor  quicksand  is  anticipated  it  is  seldom  of 
a  service  commensurate  with  the  cost.  In  sounding  for  rock 
several  methods  have  been  used. 
An  iron  rod,  upset  and  pointed  at 
one  end,  may  be  driven  to  a  depth  of 
10  or  12  feet  through  most  soils, 
and  may  be  raised  again  by  a  handle, 
as  shown  in  Fig.  3,  which  can  if 
necessary  be  fastened  to  a  lever,  a 
stout  wooden  horse  being  used  as  a 
fulcrum-.  It  is  possible  to  reach 
still  further  by  replacing  the  first 
heavy  rod  by  a  thinner  and  longer 
one  driven  in  the  same  way. 

When  there  are  not  many  boulders  or  gravel-stones  in  the 
soil  an  iron  pipe  about  I  inch  in  diameter  may  be  connected 
by  hose  with  a  fire-hydrant  and  sunk  into  the  ground  by  the 
"  jet  process"  to  a  considerable  depth.  By  connecting  the 
hose  to  the  side  of  a  T  screwed  to  the  end  of  the  pipe  and 
capping  the  top  of  this  the  pipe  can  in  most  cases  be  driven 
by  hammer  past  any  small  stones  or  other  hard  obstacles. 

A  modified  post-hole  auger  can  be  used  for  the  same  pur- 
pose, with  the  advantage  that  by  it  samples  of  the  soils  passed 
through  may  be  obtained. 


FIG.  3. — SOUNDING-ROD. 


110  SEWERAGE. 

The  only  certain  method  of  detecting  the  presence  of 
quicksand  is  by  sinking  a  test-pit,  though  the  absence  of  sand 
from  the  materials  removed  by  other  methods  would  of 
course  be  proof  of  its  absence.  The  washings  from  a  jet-pipe 
may  be  caught  and  from  the  sediment  some  idea  be  had  of 
the  materials  encountered,  though  not  of  their  consistency. 

The  presence  of  ground-water  in  any  quantity  is  fully  as 
important  a  matter  in  designing  as  the  presence  of  rock,  and 
should  be  thoroughly  investigated.  Ground-water  is  fre- 
quently found  in  porous  soils  just  at  the' base  of  a  hill.  It  is 
usually  found  in  gravelly  soils,  near  hills  or  mountain 
streams  whose  waters  percolate  into  the  porous  ground. 
Usually  (although  there  are  exceptions)  but  little  water 
reaches  the  soil  from  rivers,  whose  beds  are  in  most  cases  im- 
pervious. The  presence  and  amount  of  ground-water  can  be 
known  only  through  excavations,  which  should  be  made  with 
that  aim  in  view  if  none  exist  made  previously  for  other  pur- 
poses. In  many  cases  a  sufficient  number  of  wells  and  cess- 
pools will  have  been  dug  to  give  a  general  idea  of  the  depth 
and  amount  of  ground-water  to  be  encountered. 


CHAPTER   VII. 
THE   DESIGN. 

No  general  directions  for  designing  a  sewerage  system  can 
be  given  which  will  cover  all  the  conditions  met  with  in  every 
case.  But  upon  the  principles  stated  may  be  based  any 
special  designs,  care  being  taken  to  violate  none  of  the 
requirements  of  sanitary  sewerage.  In  many  cases  no  emer- 
gency will  arise  out  of  the  ordinary.  To  such  the  methods 
herein  outlined  apply,  but  even  in  the  use  of  these  skill  and 
judgment  must  be  employed,  and  it  may  frequently  be  neces- 
sary, as  it  is  always  desirable,  to  call  upon  the  services  of  an 
experienced  consulting  engineer  for  a  decision  as  to  some  of 
the  vital  principles  involved  in  the  design;  such,  for  instance, 
as  the  system  to  be  employed  and  the  method  of  disposal. 
But  many  small  cities  and  towns  cannot  afford  this  expense — 
or  think  they  cannot — and  the  city  engineer  must  rely  wholly 
upon  himself  for  the  design  as  a  whole  and  in  detail.  It  is 
hoped  that  the  principles  already  stated  and  the  methods  fol- 
lowing may  be  of  service  to  him. 

ART.  32.     GENERAL  PRINCIPLES. 

The  first  matter  to  be  decided  upon  in  preparing  the  design 
is,  How  much  and  what  kind  of  sewage  must  be  provided  for? 
the  second,  What  disposal  shall  be  made  of  it?  the  third, 
What  system — separate,  combined,  or  compound — shall  be 
employed  ? 

in 


112  SEWERAGE. 

It  is  assumed  that  all  urban  districts  require  house-sewer- 
age. Local  circumstances,  financial,  topographical,  and  geo- 
graphical, will  usually  decide  whether  or  not  storm-water  also 
shall  be  removed  by  the  sewers.  In  small  cities  there  are 
usually  a  few  places  the  removal  of  storm-water  from  which  is 
almost  imperative.  These  places  must  be  ascertained,  the 
area  draining  to  them  measured  on  the  contour-map,  and  an 
estimate  made  of  the  run-off  based  upon  the  principles  given 
in  Articles  18-20. 

In  towns  or  districts  which  are  closely  built  up  the  storm- 
water  should  not  flow  in  the  gutters  more  than  two  blocks  — 
or  say  700  feet — before  finding  a  sewer-inlet  or  some  natural 
stream  or  channel  into  which  it  can  discharge.  In  residence 
or  suburban  districts  the  same  rule  applies  when  the  streets 
have  impervious  pavements  and  the  yards  are  small.  As  the 
pavements  become  more  pervious  and  the  houses  more  scat- 
tered this  distance  can  be  considerably  increased  and  the 
extent  of  the  storm-sewer  system  proportionately  reduced. 
The  judgment  as  to  how  many  localities  (from  a  lack  of  water- 
courses or  other  reasons)  need  storm-sewers  must  be  balanced 
against  the  funds  available  for  such  sewers.  If  possible,  how- 
ever, the  storm-sewers  should  cover  as  wide  a  territory  as  the 
house-sewerage  system. 

In  most  small  cities  natural  watercourses  are  retained  to 
carry  away  the  run-off,  and  the  service  rendered  by  these 
may  be  made  adequate — if  it  is  not  already  so — by  enlarging, 
straightening,  and  walling  them.  (If  the  money  necessary  for 
substituting  a  storm-sewer  for  such  a  drain  is  available  this 
should  of  course  be  done.)  The  residents  along  such  a  water- 
course should  be  prohibited  from  depositing  any  excreta, 
garbage,  or  other  refuse  therein;  and  if  this  is  enforced  and 
the  stream  so  enlarged  as  to  prevent  overflowing  it  will 
become  a  good  substitute  for  a  storm-sewer,  and  much  less 
objectionable  than  such  small  streams  ordinarily  are  to  the 


THE   DESIGN.  II 3 

occupants  of  the  property  it  traverses.     For  the  amount  of 
water  to  be  provided  for  from  given  areas  see  Arts.  17-19. 

A  short  summary  of  some  of  the  principles  previously 
stated  may  be  given  here  to  advantage,  with  applications  of 
the  same. 

The  amount  of  house-sewage  depends,  first,  upon  the 
population  to  be  provided  for.  This  must  be  the  population 
some  years  in  the  future;  some  say  30,  some  50  years.  The. 
first  seems  preferable  in  most  cases,  since  the  larger  sewers^ 
called  for  by  the  second  will  be  less  suited  to  the  needs  of  the 
present,  deposits  dangerous  to  health  more  probable,  and 
consequently  cost  of  maintenance  greater;  also  in  most  cases 
the  difference  in  cost  at  compound  interest  for  30  years  would 
amount  to  sufficient  at  the  end  of  that  time  to  build  a  system, 
adequate  for  the  increased  needs.  Moreover,  the  growth  can-- 
not be  predicted  with  any  great  accuracy  30,  and  still  less  50;. 
years  ahead.  From  the  estimate  of  Baltimore's  growth  made 
by  the  Sewerage  Commission  it  is  calculated  that  to  pro- 
vide for  a  population  for  30  years  ahead  would  call  for  sewer- 
mains  of  twice  the  capacity  at  present  required;  while  if  that 
for  50  years  ahead  were  adopted  as  the  number  to  be  provided1 
for  the  mains  would  need  to  be  more  than  three  times  suchi 
capacity. 

For  making  this  prediction  it  is  customary  to  plot  alt 
known  past  populations,  each  year  and  its  corresponding 
population  being  made  coordinates  of  as  many  points.  A 
curve  is  passed  as  nearly  through  these  points  as  possible,  and 
with  the  same  law  of  curvature  is  continued  ahead  far  enough 
to  cover  the  time  required.  It  is  evident  that  such  a  curve 
should  not  return  on  itself  horizontally,  but  must  approach 
an  asymptote  whose  direction  the  judgment  must  decide;  or 
the  curve  may  in  reality  even  reverse.  This  method  is  but  a 
"  scientific  guess,"  but  there  seems  to  be  no  better  one.  As 
a  general  rule  the  smaller  the  city  or  town  the  greater  the 


114  SEWERAGE. 

probability  of  sudden  and  great  unforeseen  changes  in  the  rate 
of  growth. 

The  estimate  of  per  capita  water-consumption  is  similarly 
difficult.  There  is  no  necessity  for  this  exceeding  50  or  60 
gallons  daily,  and  yet  it  may  reach  200  or  even  300  for  any- 
thing which  we  know  to  the  contrary.  Since  it  can  be  con- 
fined well  within  the  100  mark  by  the  use  of  meters  and 
thorough  inspection,  it  seems  wasteful  of  capacity  and  capital 
to  provide  for  more.  The  probability  is  that  the  near  future 
will  see  the  consumption  almost  universally  reduced  below 
this  limit. 

The  population  decided  upon  times  the  per  capita  water- 
consumption  and  plus  the  leakage  may  be  taken  as  the 
amount  of  sewage  to  be  provided  for. 

The  character  of  the  sewage,  involving  the  proportionate 
amount  of  house-wastes  and  diluting-water,  the  character  of 
the  water  supplied,  the  presence  of  acids  or  other  manufac- 
turing wastes,  will  have  a  bearing  upon  the  method  of  dis- 
posal. 

In  deciding  upon  the  disposal  to  be  adopted,  if  that  by 
dilution  is  practicable  the  laws  of  the  State  should  be  investi- 
gated to  determine  its  legality;  the  direction  and  velocity  of 
tides  and  currents  should  be  known  to  be  such  as  to  remove 
the  sewage  continuously  from  rather  than  toward  all  shores 
or  other  places  where  it  may  be  deposited  and  create  a 
nuisance;  the  number  of  gallons  of  unpolluted  water  passing 
the  outlet  each  day  should  be  equivalent  to  at  least  1500 
times  the  population;  the  velocity  of  the  water  past  the  out- 
let must  be  sufficient  to  prevent  the  deposit  of  sewage  matter 
at  or  near  said  outlet.  The  effect  of  the  discharge  upon 
bathing-beaches,  upon  fish,  oysters,  or  other  food  matter, 
upon  the  water-supply  of  towns  below,  or  upon  manufactur- 
ing interests — these  must  all  be  studied,  both  on  their  scien- 
tific and  commercial  sides. 


THE   DESIGN.  115 

If  from  these  investigations  dilution  is  found  inadvisable 
the  method  of  treatment  best  adapted  to  the  circumstances 
must  be  sought.  Search  should  be  made  for  a  spot  or 
spots  which  are  low  and  flat,  but  not  boggy,  whose  soil  is 
pervious  and  whose  value  is  low  (although  land  which  pos- 
sesses none  of  these  qualities  can  be  used  for  sewage  disposal), 
and  whose  extent  is  sufficient  for  years  to  come.  If  the 
sewage  must  be  thoroughly  purified  filtration  or  irrigation 
must  be  used,  alone  or  in  connection  with  precipitation  or 
septic  tanks.  Chemical  precipitation  may  be  employed  alone 
where  a  removal  of  50$  to  65$  of  the  impurities  will  be  suffi- 
cient. (See  the  works  on  sewage  purification  referred  to  in 
Chapter  II,  which  should  be  diligently  studied  before  decid- 
ing upon  any  scheme  of  treatment.) 

It  will  usually  be  well  to  make  preliminary  plans  based 
upon  each  of  two  or  three  methods  of  disposal  and  compare 
them  from  both  sanitary  and  financial  points  of  view. 

A  decision  as  to  the  system  to  be  employed  should  ordi- 
narily rest  largely  upon  the  decisions  of  the  two  previous 
points.  If  treatment  of  the  sewage  is  necessary  or  will 
probably  become  so  in  the  course  of  20  or  30  years,  or  if  the 
house-sewage  is  to  be  discharged  at  some  distance  from  the 
centre  of  the  city,  the  separate  or  compound  system  will 
usually  be  advisable. 

If  there  are  a  number  of  convenient  points  along  a  water 
front  at  each  of  which  house-sewage  can  be  discharged  with- 
out nuisance  the  combined  system  may  be  the  cheapest  and 
most  desirable.  If  there  already  exist  large  sewers  discharg-, 
ing  at  various  points  where  the  discharge  of  house-sewage 
creates  a  nuisance,  or  of  a  character  not  adapted  to  carrying 
house-sewage  (because  of  flat  bottoms  or  rough  interior),  the 
separate  system  will  usually  be  advisable,  the  old  sewers 
being  used  in  the  storm-sewer  system.  If  such  large  sewers 
are  adapted  in  interior  surface  and  form  to  carrying  house- 


Il6  SEWERAGE. 

sewage,  however,  they  may  be  retained  for  this  purpose,  but 
an  intercepting  sewer  built  to  receive  from  them  the  dry- 
weather  flow  and  convey  it  to  a  suitable  outlet,  the  storm- 
water  discharging  through  the  previous  outlets. 

In  all  these  matters,  however,  engineering  experience  and 
judgment,  and  not  fixed  rules,  should  be  the  basis  of  decision. 

The  general  rule  in  sewerage,  as  in  other  engineering  work, 
is:  obtain  the  best  results  and  at  the  least  cost.  Certainty 
of  attaining  this  will  frequently  require  the  preparation  and 
comparison  of  alternative  plans,  both  of  the  system  as  a 
whole  and  of  its  separate  parts. 

ART.  33.     SUBDIVISION  INTO  DISTRICTS. 

For  the  purpose  of  sewerage-designing  the  territory  under 
consideration  is  ordinarily  divided  into  two  sets  of  districts, 
one  based  upon  the  density  of  population,  the  other  upon  the 
slope  of  the  ground-surface. 

The  former  division  should  take  as  a  basis  the  probable 
density  of  population  per  acre  of  different  sections  at  some 
time — say  30  years — in  the  future,  since  the  system  must 
serve  the  population  at  that  time  as  well  as  in  the  present. 
It  will  be  convenient  to  base  the  division  upon  population  per 
acre  of  20,  30,  and  other  factors  of  10,  20  being  the  minimum 
assumed  for  habitable  districts  in  most  cities.  The  maximum 
may  run  up  to  150  or  more  per  acre.  As  this  division  is  for 
the  purpose  of  design  only  and  is  not  usually  shown  upon  the 
finished  map,  it  may  be  designated  by  bounding-lines  or  by 
tints  upon  a  working  map.  (It  will  be  well  to  have  several 
copies — white  or  blue  prints  will  do — of  the  city  map  as  work- 
ing maps.)  Having  made  the  above  subdivision,  the  total 
population  of  each  area,  calculated  from  the  assumed  density 
of  population,  should  be  ascertained,  and  the  sum  of  all  these 
compared  with  the  future  total  population  as  estimated  by  use 


THE   DESIGN.  1 1/ 

of  the  curve  (Art.  32).  It  may  exceed  this  by  a  small 
amount — say  10$ — to  allow  for  incorrect  apportioning  of 
densities.  If  it  does  not  at  least  equal  it  changes  in  the 
extent  of  the  different  areas  should  be  made  sufficient  to  give 
this  total  and  at  such  points  as  the  engineer's  best  judgment 
dictates. 

The  second  subdivision  is  that  into  drainage  districts. 
For  this  purpose  a  carefully  prepared  contour-map  of  the  city 
or  area  to  be  sewered  is  necessary.  Each  district  is  to  con- 
tain all  the  territory  draining  into  one  main  sewer,  together 
with  that  main  down  to  its  outlet  or  junction  with  the  inter- 
cepting or  outlet  sewer.  Under  some  plans  of  sewer  assess- 
ments this  subdivision  is  necessary  for  other  than  engineering 
purposes.  For  house-sewers  it  can  usually  be  best  made 
after  the  designing  of  the  sewers  is  completed.  For  storm- 
sewers,  however,  it  should  be  made  after  the  lines  are  located, 
but  before  the  sizes  are  determined  upon,  to  facilitate  calcu- 
lation of  the  latter. 

ART.  34.     LOCATING  THE  SEWER-LINES. 

Unless  this  location  is  already  occupied  by  gas-  or  water- 
pipes  or  a  street-railroad  house  and  combined  sewers  are  in 
most  cases  located  in  the  centres  of  streets  or  alleys,  the  cost 
to  the  householders  on  each  side  for  house-connections  being 
thus  made  equal.  In  some  cities  the  sewers  are  located  under 
the  sidewalks,  there  being  a  line  on  each  side  of  the  street. 
This  plan,  which  is  used  at  Washington,  D.  C.,  quite  exten- 
sively, is  usually  adopted  in  the  case  of  wide  streets,  since 
there  the  cost  of  the  extra  line  is  less  than  that  of  the  addi- 
tional lengths  of  house-connections  required  by  a  single  sewer. 
From  a  financial  standpoint  the  double  line  is  cheaper  when 
the  cost  of  a  minimum-sized  sewer  (6-  or  8-inch)  of  a  length 
equal  to  the  average  house-lot  frontage  is  less  than  the  cost 


Il8  SEWERAGE. 

of  a  house-connection  of  a  length  equal  to  the  distance 
between  the  two  sewer-lines.  Another  advantage  of  side 
sewers  is  that  the  street-paving  need  not  be  torn  up  in  making 
house-connections.  A  serious  disadvantage  is  that  the  dis- 
tance from  the  upper  end  of  each  line  to  the  point  where  the 
sewage  flow  is  self-cleansing  in  volume  and  velocity  will  be 
double  that  when  but  a  single  line  is  laid.  Also  the  roots  of 
shade-trees  are  apt  to  cause  serious  trouble  by  entering  the 
pipe-joints.  Probably  the  best  method  of  avoiding  both 
these  last  objections  and  that  of  the  continual  tearing  up  of 
the  street-pavement  is  to  lay  the  sewer  in  the  street  centre 
and  at  the  same  time  carry  each  house-connection  to  the  curb. 

Where  a  city  has  alleys  intermediate  between  the  streets 
it  may  sometimes  be  advisable  to  carry  the  sewers  through 
these  rather  than  through  the  streets,  the  principal  argument 
for  this  being  that  less  valuable  paving  is  destroyed  and  less 
obstruction  caused  to  traffic  by  the  work  of  construction. 
On  the  other  hand  the  house-connection  will  be  longer,  and 
both  the  cost  increased  and  the  grade  in  such  connection 
decreased,  if  the  distance  from  the  house  to  the  street  centre 
is  less  than  that  to  the  alley  centre,  as  is  generally  the  case. 
Moreover,  the  paving  in  an  alley  should  be  equally  as  good  as 
that  in  a  street,  and  the  unevenness  consequent  on  sewer 
construction  is  exceedingly  apt  to  contribute  to  the  disease- 
breeding  slovenliness  in  what  is  often  at  its  best  an 
elongated  Gehenna.  Again,  in  a  narrow  alley  the  space 
available  for  piling  the  excavated  dirt  is  so  contracted  that  the 
cost  of  construction  is  frequently  increased  by  a  very  appre- 
ciable amount  on  this  account.  On  a  side  hill,  however,  it 
may  often  be  advisable  or  even  necessary  to  locate  sewers  in 
the  alleys  for  the  drainage  of  houses  on  the  lower  sides  of 
streets  above. 

Sewers  should  be  laid  in  continuous  straight  lines,  as  far 
as  possible. 


THE  DESIGN. 


No  turn  greater  than  a  right  angle  should  be  made  at  any 
one  point  by  any  sewer  less  than  24  inches  in  diameter,  and 
any  turn  whatever  made  by  such  a  sewer  should  be  in  a  man- 
hole, by  means  of  a  curved  channel.  For  sewers  larger  than 
12  or  15  inches  it  is  advisable  to  use  two  manholes  in  making 


15 


30' 


FIG.  4. — ALIGNMENT  OF  SEWER-JUNCTIONS. 

a  bend  greater  than  45°  (see  Fig.  4).  Brick  sewers  more 
than  24  inches  in  diameter  may  be  laid  on  curves,  since  they 
can  be  entered  for  inspection  or  cleaning. 

Each  lateral  sewer  should  take  the  most  direct  course  to 
its  main,  each  main  the  most  direct  course  to  its  outlet,  and 
the  number  of  mains  should  be  as  few  as  possible.  This 
serves  both  economy  and  sanitary  efficiency. 

The  dead  ends  should  be  made  as  few  as  possible,  even  at 
some  expense  of  additional  excavation,  but  not  by  reducing 
mean  velocities  below  2.5  feet  per  second;  nor  is  it  ordinarily 
serviceable  to  unite  the  upper  ends  of  sewers  flowing  in  oppo- 
site directions. 

House-sewers  should  be  carried  within  reach,  as  regards 
both  horizontal  distance  and  grade,  of  every  lot  in  the 
sewered  district. 

Storm-sewers    should    have  as    few    branches  as   can    be 


120         •  SEWERAGE. 

made  to  reach  all  the  street-inlets,  to  better  insure  which  such 
inlets  should  be  located  previous  to  the  location  of  the  sewer- 
lines. 

It  is  generally  advisable  to  avoid  crossing  private  property 
where  possible,  since  legal  complications  and  delays  might 
result  from  such  crossing.  This  will  frequently  be  impossible, 
however,  particularly  near  outlets. 

The  sewer-lines  can  usually  be  laid  out  directly  upon  a 
contoured  working  map,  an  approximate  rough  estimate  of 
the  necessary  size  and  consequent  minimum  slope  of  each 
sewer  being  made,  that  deep  or  shallow  cutting  may  be 
avoided.  The  direction  of  flow  should  be  indicated  by 
arrows. 

In  the  separate  system  the  storm-water  sewers  should 
usually  be  placed  on  one  side  of  the  street  centres,  the  house- 
sewers  being  placed  in  the  centres.  The  two  should  never  be 
placed  one  above  the  other  in  the  same  trench  unless  in  con- 
tact with  each  other  or  connected  by  masonry. 

ART.  35.     VOLUME  OF  HOUSE-SEWAGE. 

Since  the  grade  of  a  sewer  is  limited  by  its  size,  and  the 
size  is  determined  by  the  grade  and  consequent  velocity,  but 
to  even  a  greater  extent  by  the  maximum  volume  of  sewage 
to  be  carried,  this  last  must  be  determined  before  either  the 
limiting  grade  or  size  can  be  decided  upon.  If  the  maximum 
rate  of  water-consumption  be  taken  at  175  gallons  per  day 
per  capita  the  maximum  volume  per  second  to  be  carried  by 

a.  sewer  (in  cubic  feet)  is ^ ^> ,  in  which  D  =  density 

of  population  and  A  =  the  area  in  acres. 

Beginning  at  the  summit  of  each  lateral,  it  is  clear  that  it 
is  unnecessary  to  calculate  the  capacity  required  for  any  sec- 
tion of  sewer  until  the  point  is  reached  where  the  volume  of 


THE   DESIGN.  121 

sewage  to  be  carried  exceeds  the  capacity  of  the  smallest 
sewer  used  at  the  given  grade.  For  an  8-inch  pipe  flowing 
half  full  with  an  average  velocity  of  2.5  feet  per  second  this 

/3.I4I6  X  16  X  2.5       \ 
volume  is    about    ^—    — -  =  Jo. 4363  cubic  feet 

per  second,  which  would  be  contributed  as  a  maximum  flow 

^0.4363  X  7.48  X  86400       \ 
by   a   population    of    (  -  -  =  yi6n,    or 

about  40  acres  having  a  density  of  population  of  40. 

At  the  point  where  the  sewage  from  the  tributary  popula- 
tion exceeds  the  capacity  of  the  sewer  its  size  must  be 
enlarged  to  the  next  market  size  of  pipe  or  the  next  size  of 
brick  sewer  convenient  for  construction. 

The  allowance  for  leakage  into  the  sewer  of  ground-water, 
which  should  be  a  small  proportion  of  the  sewage  proper,  may 
be  added  at  intervals,  according  to  the  engineer's  judgment, 
based  on  such  data  as  he  is  able  to  obtain. 

In  calculating  these  volumes  it  is  advisable  to  begin  with 
the  furthermost  lateral  sewer  first;  where  this  joins  another 
the  contributions  of  both  are  to  be  added  to  determine  the 
flow  below  that  point,  and  in  tracing  down  this  line  as  each 
branch  is  encountered  its  contribution  must  be  calculated  and 
added.  Decision  having  been  made,  after  a  study  of  the 
topographical  map,  as  to  the  line  of  sewer  into  which  each 
section  of  undeveloped  territory  will  drain  when  sewered,  the 
sewage  which  this  area  will  ultimately  contribute  should  be 
placed  at  the  heads  of  the  volumes  of  flow  in  this  line. 

An  excellent  method  of  making  these  calculations  is 
shown  on  page  122.  The  sewerage-map  Plate  No.  Ill  was 
used  for  this  table. 

In  this  case  it  is  seen  that  the  capacity  of  an  8-inch  pipe 
at  the  minimum  grade  was  reached  at  the  junction  of  the 
Newcastle  and  Budd  Street  sewers,  but  the  line  down  Budd 
has  i  :  50  as  its  grade,  and  no  increase  of  size  is  yet  necessary. 


122 


SEWERAGE. 


CALCULATION    OF    SEWAGE    QUANTITIES    AND    SEWER    SIZES. 


Street. 

From 

To 

a 

<< 

Density. 

er!   i 

11 

o  ~ 

Sewage. 
Gallons 
per  Day. 

Total 
Sewage. 

V 

•o 
rt 

O 

ij 

j/5 

Prospect 

Walnut 
Walnut 
Liberty  (extended) 
Walnut 

Newcastle 

Prindle 
Prospect 
Newcastle 
Liberty 

Walnut 

Prospect 
Liberty 
Walnut 
Budd 

10.4 

i-7 
1.9 
12.7 

8.2 

20 

20 

20 
2O 
20 

208 

34 
38 
254 
164 

36400 

5950 
6750 
44450 
28700 

52So 
9555° 
26250 
154000 

122250 

J         30 
(        " 

20 
2O 

300 
I       300 

Sin. 

Newcastle 
Undeveloped   terri 
Newcastle 
Undeveloped   terri 

Prospect 
tory  tnbuta 
Liberty 
tory  tributa 

Liberty 
ry  to  Newcastle 
Budd 
ry  to  Budd 

i-5 
27-3 
7-5 
44.0 

20 
2O 
20 
2O 

£ 

150 

880 

I       300 
I       50 

Sin.. 
8  in. 

10  " 

281050 

Budd 
Budd 
Budd 

Newcastle 
Walnut 
Walnut 

Walnut 
River 
River 

II.  O 

3-o 
Gro 

2O 
2O 

und- 

220 

60 

water 

38500 

319550 

10500 

452300 

At  the  junction  of  Budd  and  Walnut  the  sewage  amounts  to 
441,800  gallons,  or  40.9  cubic  feet  per  minute,  and  the  sev/er 
from  there  to  the  river  must  have  the  minimum  grade  allow- 
able. The  size  must  therefore  be  increased,  and  as  the  next 
market  size,  lo-inch,  has  a  capacity  at  that  grade  when  two- 
thirds  full  of  about  590,000  gallons,  it  is  therefore  sufficiently 
large  for  the  rest  of  the  line,  including  sewage  contributed 
along  its  length  and  ground-water.  No  ground-water  was 
anticipated  on  the  hill  side,  but  it  was  considered  probable 
that  on  Budd  below  Walnut  this  would  leak  into  the  sewer  at 
the  rate  of  two  gallons  per  day  per  foot  of  sewer  (see  Art. 
46). 

ART.  36.     VOLUME  OF  STORM-SEWAGE. 

The  principles  stated  in  Articles  16-20  will  be  used  as  a 
basis  in  determining  the  amount  of  storm-water  to  be  pro- 
vided for.  Decision  should  first  be  made  as  to  whether  this 
shall  include  run-off  from  storms  of  the  first,  second,  or  third 
class.  Then  the  past  rates  of  fall  of  such  storms  should  be 
ascertained.  If  the  records  of  such  rates  extending  over  a 
series  of  years  are  not  obtainable  use  may  be  made  of  the 
rainfall  data  given  in  Art.  17.  Plate  No.  IV  shows  rainfall- 
curves  for  average  maximum  rains  of  the  second  class,  from 


THE  DESIGN. 


123 


Plate  III. 


124  SEWERAGE. 

which  may  be  taken  the  amount  of  rain  to  be  expected  during 
any  given  period  of  time  in  the  localities  named.  If  sufficient 
rainfall  data  for  the  place  in  question  are  available  a  similar 
curve  for  that  place  plotted  from  these  data  will  be  found 
serviceable.  If  these  data  have  not  been  kept  by  the  city  it 
is  probable  that  the  rates  for  a  neighboring  city  can  be 
obtained  from  the  Weather  Bureau  at  Washington,  which  now 
has  self-registering  gauges  in  over  fifty  cities  of  the  United 
States. 

Next  to  be  determined  is  the  character  of  surface  of  the 
streets  and  included  areas  in  each  section  drained ;  that  is,  the 
amount  of  impervious  surface.  The  safest  course  would  be 
to  assume  that  every  street-surface  is,  or  will  be  made,  wholly 
impervious;  that  the  space  covered  by  each  building  will  also 
be  impervious;  and  that  in  residence  districts  the  remaining 
areas  will  be  30$  to  80$  impervious  at  the  time  of  heavy 
downpours,  since  rainfall  records  show  that  at  least  25$  of 
these  are  preceded  by  one  or  more  hours  of  rainfall,  which 
increase  the  natural  imperviousness.  These  figures  will  be 
used  in  illustrative  calculations  in  this  work;  but  the  judgment 
of  the  engineer,  based  on  local  conditions,  may  well  dictate 
others,  differing  for  each  case  considered.  For  instance,  a 
closely  built-up  business  district  having  paved  yards  and 
courts  may  be  assumed  as  all  wholly  impervious. 

These  points  having  been  decided,  the  inlets  should  be 
located  on  a  contour-map.  Also  it  will  be  well  to  state  in 
figures  on  each  city  block  its  area  and  percentage  of  imper- 
viousness (see  Plate  V). 

The  percentage  of  imperviousness  may  be  calculated  thus: 

Let  /  =  the  average  length  of  a  city  block- 
b=    "        "          breadth  "     " 

/=    "  number  of  front  feet  to  a  building- 

lot; 
d=    "        "          depth  of  a  building-lot; 


THE  DESIGN. 


I25 


DURATION  OF  RAIN   IN   MINUTES. 
20  30  40  50 


1300 


1200 


1100 


RATES  OF  RAINFALL 
STORMS  OF  THE 
SECOND  CLASS. 


CURVE  FOR  OBTAINING 
AREA  IN  ACRES. 


100 


700 


6UO 


500  400  300  200 

WIDTH  OF  AREA  IN   FEET. 


100 


126  SEWERAGE. 

a  —  the  average  area  covered  by  a  building: 
w—    "        "          width  of  street; 

i  =•    "  percentage  of  imperviousness  of  yards, 

courts,  etc.,  expressed  as  a  decimal; 

/=•"     percentage   of   imperviousness   of  the   entire 

area,  expressed  as  a  decimal. 
Then 


+  w) 


lb-\-  w(l-\-b  +  w) 

lb(a  4-  jfd  -  ig)  -f  Wfd(l  +  b  +  w) 


As  an  example,  let  7=450,  £  =  250,  /  —  50,  d=  125, 
a  =  1200  sq.  ft.,  w  —  66,  i  =  .60;  then  /=  -777,  or  say  .78. 

When  most  of  the  above  factors  must  be  estimated  by 
judgment  only,  as  for  areas  not  yet  opened  up  or  fully  devel- 
oped, it  may  be  as  well  to  estimate  /at  once. 

By  comparing  this  formula  with  that  on  page  36  we  see 
that 

lb(a  +  ifd  -  ia)  +  wfd(l  +  b  +  w) 


which  formula  can  be  used  when  P  has  already  been  calcu- 
lated. The  relation  between  /  and  P  will,  it  is  evident,  vary 
in  different  cities  and  also  in  different  parts  of  the  same  city. 
The  map  having  been  thus  prepared,  with  the  a  and  /  on 
each  block,  the  uppermost  corner  of  the  drainage-area  furthest 
from  the  outlet  may  be  taken  as  a  starting-point.  If  there 
are  beyond  this  any  areas  not  included  in  the  sewered  districts, 
but  the  run-off  from  which  flows  into  such  districts,  this  run- 
off must  be  estimated  and  provided  for.  For  this  purpose  the 
formula  Q  =  AIR  may  be  used,  A  being  the  total  area,  /  the 
coefficient  of  imperviousness,  and  R  the  maximum  rate  of 
rainfall  (of  the  class  to  be  provided  for)  for  that  length  of 


THE   DESIGN.  I2/ 

time  which  will  elapse  while  the  run-off  from  the  furthest 
point  of  the  drainage-area  is  reaching  the  sewer.  This  time 
is  an  uncertain  quantity  and  will  to  a  certain  extent  vary 
with  R.  Some  engineers  assume  a  velocity  of  about  2  feet 
per  second  over  the  surface.  The  formula  v  =  lOOofVS  is 
offered  as  an  empirical  one  for  calculating  the  velocity  of 
run-off  over  the  surface  in  feet  per  minute,  5  being  the  sine 
of  the  slope.  While  7  does  not  directly  affect  this  velocity, 
it  is  observed  that  the  most  impervious  surfaces  usually  offer 
the  least  obstruction  to  the  flow  of  water,  and  vice  versa. 
The  time  /  for  which  R  is  assumed  is  obtained  by  dividing 
i>  into  L,  the  length  of  the  furthest  corner  of  the  drainage-area 
from  the  sewer. 

The  same  method  is  also  applied  to  determining  the  time 
of  run-off  from  each  smaller  area  to  its  inlet,  L  in  such  cases 
being  taken  as  the  distance  by  gutter  of  the  furthest  point 
from  its  inlet. 

The  amount  of  run-off  to  each  point  of  interception  thus 
found  must  be  provided  for  by  inlets  of  sufficient  size  and 
number  (see  Art.  41)  and  by  ample  sewer  capacity.  The  fol- 
lowing tabulation  of  a  calculation  by  the  above  method  for 
the  district  shown  in  Plate  V  is  given  as  an  illustration,  a  is 
the  size  of  each  sub-area,  /its  imperviousness;  AI  is  in  each 
case  the  sum  of  all  the  preceding  af's.  s  is  the  surface-slope 
of  the  sub-area,  /  is  the  greatest  distance  traversed  by  the 
run-off  in  crossing  each  sub-area,  /  is  the  time  occupied  by 
the  run-off  in  travelling  the  distance  /,  r  is  the  rate  of  rainfall 
for  the  time  t,  q  =  air.  S  is  the  slope  of  the  sewer  removing 
the  run-off  from  the  point  in  question,  L  its  length  to  the 
point  next  considered  (usually  the  next  inlet  or  sewer-junc- 
tion), T  is  the  time  occupied  by  the  run-off  in  flowing  from 
the  extreme  limit  of  the  entire  drainage-area  A  over  the  sur- 
face and  through  the  sewers  to  the  point  under  consideration, 
R  is  the  rate  of  rainfall  for  the  time  T,  Q  is  the  total 


128 


SEWERAGE. 


Plats  V, 


1ST 


°>£< 

Sol1 

is* 


STREET 


*• 

\ 

*3 

#3 

a=2.5      "i 

OQ 

a=2.5 

I=.80        j 

. 

J=.80 

I=.80 

i 

9 

fc 

17 

V 

in 

2ND        f 

»„ 

STREET 

42"   S  =  .006 

f' 

III 

#4 

#5 

coj 

=^6 

a=3.6      «g 

GO 

a=3.6 

4 

a=3.6 

Q 

I=.8U 

I=.80 

1 

7=.80 

1 

E 

^1 
i 

n                             n 

3RD  3  y*~        2j'"s  =  .008       /           52"  S=."ob4 

T-  STREET 

D 

*7 

LU 

ID 

UJ 

ID 

c 

#9 

UJ 

D 

•^ 

z 

•7- 

7" 

a=3.6      § 

LJ 

a  =3.0 

UJ 

a=3.6 

LU 

J=.80 

> 

< 

7=.80 

> 

< 

4TH 


STREET 


>     DIRECT1ONJOF  FLOW  ( 

Q  INLET 

•  MANHOLE  I 


THE  DESIGN. 


I29 


0          ON 

'o      'cT 

s   s 

cr      cr 

CO        0\         ^I         4- 

r 

to 

p 

M 

Undeveloped  territory 

0 

2, 

1 

M              M 
CO           GO 

CO          CO          CO          CO 

to 

to 
en 

to 

en 

* 

n 

CO          CO 

O        O 

CO          CO          CO          CO 

0000- 

'co 

'o 

i? 

81 

s 

M              M 

to        to        to        to 

to 

to 

to 

4^ 

„ 

£    £ 

CO          CO           CO           CO 

CO           CO           CO           CO 

O 

0 

0 

•>, 

-u        to 

M         co       en        to 

10           4^-            ON          GO 

0 

to 

GO 

» 

* 

fe 

8     8 

^j        ui 

8b       b       b 
O         O         M 
^j        en        ^j        Co 

g 

b 

M 

b 

M 

b 

en 

- 

O1*         O^ 
OJ          Oi 

O          O 

CO           CO           CO          CO 

8800 

to 
en 

ON 
M 

en 

en 

CO 

8 

- 

ON           0 

O            >H           O           ***4 

ON         4^-           O           CO 

to 

M 

to 

M 
M 

- 

CO           CO 

io        b 

co        to        to       co 

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Location  of  Sewer. 

1 30  SE  WERA  GE. 

amount  of  run-off  from  all  the  drainage-areas  above  =  AIR. 
q(=  air)  as  well  as  Q  should  be  calculated  for  each  sub-area, 
and  if  the  Q  for  any  stretch  of  sewer  is  at  any  place  less  than 
the  q  immediately  tributary  to  the  same  the  latter  should 
determine  the  size. 

Plate  IV  will  be  found  convenient  for  determining  a,  and 
also  R  when  the  rates  of  rainfall  of  the  place  in  question  can 
be  represented  by  any  of  the  curves  there  given,  these  being 
for  rains  of  the  second  class.  To  find  a  in  acres  from  the 
diagram,  use  one  dimension  (in  feet)  of  the  area  (or  of  an 
equivalent  rectangle  if  it  is  not  rectangular)  as  an  ordinate 
and  find  the  corresponding  abscissa  of  the  acre-curve  in  the 
diagram ;  divide  this  into  the  other  dimension  of  the  area  and 
the  quotient  will  be  a  in  acres. 

By  the  table  the  run-off  from  the  undeveloped  territory  is 
placed  at  55.2  cubic  feet  per  second,  which  is  carried  by  a 
42 -inch  sewer  on  a  .6$  grade  for  360  feet,  where  it  receives 
still  more  sewage,  the  maximum  amount  to  be  received  there, 
both  over  the  surface  and  through  the  sewer,  being  57.2  cubic 
feet,  although  q  for  the  block  No.  I  alone  is  6.8  cubic  feet. 
But  Q  is  not  equal  to  55.2  +  6.8,  because  the  latter  quantity 
was  due  to  a  rainfall  of  6.25  minutes'  duration,  or  rather  to 
the  maximum  rate  for  that  time,  during  which  only  such 
water  would  have  arrived  from  the  upper  end  of  the  drainage- 
area  as  was  due  to  a  lower  rate  of  rainfall;  but  the  time  of 
16.9  minutes  is  that  for  which  the  run-off  is  calculated  from 
both  the  undeveloped  territory  and  block  No.  I.  Blocks 
No.  2  and  No.  3  both  reach  the  sewer  at  the  same  point,  and, 
taking  the  rate  of  rainfall  for  17.7  minutes,  we  have  a  total 
run-off  from  all  the  territory  above  of  66  cubic  feet  per  second 
and,  the  grade  being  .5$  a  44-inch  sewer  is  found  to  be 
necessary. 

Blocks  No.  4  and  No.  7  discharge  first  into  a  branch 
sewer,  which  it  is  found  should  be  24  inches  in  diameter. 


THE  DESIGN.  131 

Where  this  joins  the  main  the  run-off  from  blocks  No.  5  and 
No.  8  and  from  half  of  No.  6  and  No.  9  also  reaches  it,  and  it 
must  consequently  be  increased  in  size.  The  time  T  at  this 
point  is  1 6. 1  -f~  °-  8  (in  the  Ave.  B  sewer)  -|-  0.8  (in  the  Second 
Street  sewer)  -f-  1.4  (in  the  Ave.  C  sewer),  or  19.1  minutes, 
and  the  rate  of  rainfall  for  this  time  is  used  for  the  run-off 
from  the  entire  area. 

It  will  be  seen  that  the  method  here  employed  is  but  a 
practical  application  of  the  principles  stated  in  Art.  18. 
More,  and  more  accurate,  data  for  determining  t  and  /,  as 
well  as  R9  are  needed  before  this  or  any  method  can  be  relied 
upon  to  give  more  than  general  approximations  to  the  run-off. 
Fortunately  with  the  method  here  given  the  approximation 
becomes  more  close  as  the  area  becomes  more  urban,  and  is 
most  so  in  the  most  densely  populated  districts,  where  the 
danger  from  gorged  sewers  would  be  greatest. 

ART.  37.     GRADE,  SIZE,  AND  DEPTH  OF  SEWERS. 

For  both  determining  and  recording  the  grades  of  the 
proposed  sewers  use  is  usually  made  of  the  profiles  of  the 
streets,  plotted  from  the  level  notes.  Upon  these  a  vertical 
longitudinal  section  of  the  proposed  sewer  through  its  centre 
line  is  placed,  thus  showing  the  size,  grade,  and  depth  of  the 
sewer.  While  designing,  however,  it  will  be  found  convenient 
to  pencil  in  the  line  of  the  invert  only,  since  then  changes  in 
its  vertical  location  can  more  readily  be  made. 

A  short  experience  in  sewer-designing  will  demonstrate 
how  mutually  involved  are  Q,  S,  the  diameter  and  the  depth 
of  the  sewer.  In  many  cases  it  will  be  necessary  to  alter  and 
realter  the  grade  and  diameter  before  obtaining  for  each  reach 
of  sewer  the  best  obtainable  depth  and  velocity.  Q  is  a  fixed 
quantity  for  any  given  case,  5  may  vary  between  fixed  limits, 
the  size  also  has  its  limits  in  some  cases,  but  the  depth  of  the 


I32  SEWERAGE. 

sewer  may  vary  from  any  distance  below  to  any  distance  above 
ground.  A  depth  of  25  or  30  feet  is  obtained  in  many 
sewerage  systems,  and  even  50  feet  or  more  has  been  reached 
in  open  cut,  while  sewers  have  been  laid  in  tunnel  at  still 
greater  depths.  Where  possible  deep  sewers  should  run 
through  wide  streets,  that  the  danger  to  building-foundations 
may  be  kept  as  small  as  possible;  and  they  should  avoid  the 
busiest  thoroughfares  unless  these  are  also  the  widest  streets 
and  the  soil  is  treacherous.  The  sewer  may  in  some  cases  be 
carried  on  bridges  or  trestles,  as  in  crossing  a  stream  or  ground 
lower  than  the  hydraulic  gradient.  In  many  such  locations, 
however,  this  position  will  be  impossible,  owing  to  traffic  on 
the  river,  to  danger  from  floods,  to  blocking  of  streets,  or  to 
prohibitive  cost  of  construction.  In  such  cases  the  pipe  may 
be  placed  under  the  surface  of  the  ground  or  in  the  bed  of 
the  stream,  being  thus  below  the  hydraulic  gradient.  Such  a 
downward  loop  is  called  an  inverted  siphon.  Many  instances 
of  these  are  in  use,  and  if  care  be  taken  in  their  design  and 
construction  they  need  give  no  trouble.  It  will  not  be  possi- 
ble, or  at  least  advisable,  to  connect  any  buildings  to  an 
inverted  siphon,  since  the  sewage  will  continually  stand  in 
the  connections  up  to  the  level  of  the  hydraulic  gradient  of 
the  siphon. 

The  depth  of  storm-sewers  is  usually  fixed  by  grade 
requirements  only;  the  covering  over  them,  however,  should 
be  not  less  than  two  feet  and  would  better  be  three  or  four 
feet.  The  minimum  depth  to  which  house  or  combined 
sewers  should  be  laid  will  usually  be  decided  by  local  circum- 
stances or  customs.  It  is  generally  desirable  to  lay  them 
somewhat  deeper  than  the  gas-  or  water-pipes,  that  these  may 
not  interfere  with  them.  The  city  of  Brooklyn  some  years 
ago  fixed  12  feet  as  the  depth  to  which  all  (combined)  sewers 
are  to  be  laid,  unless  the  maintenance  of  proper  velocity 
requires  a  less  or  greater  one.  In  Philadelphia  14  feet  is  the 


THE  DESIGN.  133 

standard  depth,  in  Washington,  D.  C.,  10  feet.  In  residence 
districts  in  the  smaller  cities  7  to  10  feet  is  usually  sufficient, 
although  in  a  street  running  along  a  hillside  a  much  greater 
depth  may  be  called  for  by  the  depth  of  basements  upon  the 
lower  side  of  the  street.  In  streets  which  are  already  built 
up  the  sewer  should  be  deep  enough  to  drain  all  basements 
and  cellars,  with  the  exception,  perhaps,  of  an  occasional  one 
of  unusual  depth.  To  insure  this  the  cellar  depths  taken 
during  the  survey  should  be  indicated  in  their  proper  positions 
upon  the  profiles  of  their  respective  streets.  In  many 
Southern  cities  where  there  are  no  cellars  under  the  dwellings 
and  there  is  little  danger  of  frost  the  sewers  may  be  given  a 
depth  of  covering  of  only  3  or  4  feet.  In  the  North  6  feet  is 
probably  the  least  depth  which  should  be  given  to  the  flow- 
line  save  under  exceptional  circumstances.  The  maximum 
depth  should  be  kept  at  14  to  16  feet  if  possible,  since  below 
this  the  cost  rapidly  increases.  When  the  depth  is  consider- 
able the  expense  of  making  house-connections  may  become 
excessive.  It  may  in  such  cases  be  found  cheaper  to  lay  a 
small  sewer  about  7  or  8  feet  below  the  surface  and  following 
the  surface  grade,  which  may  be  with  or  against  the  grade  of 
the  deep  sewer,  to  a  manhole  in  the  deep  sewer  into  which 
this  shallow  one  can  discharge. 

Before  fixing  the  grade  it  is  well  to  prepare  tables  similar 
to  those  given  in  Articles  35  and  36,  and  also  to  calculate  as 
closely  as  possible  the  total  amount  of  sewage  reaching  each 
outlet. 

Very  often  the  main  sewer  for  a  long  distance  from  the 
outlet  must  be  laid  at  a  minimum  grade  if  pumping  is  to  be 
avoided  or  the  lift  kept  as  small  as  possible.  In  such  a  case 
the  grade  of  this  main  will  be  the  first  to  be  located  upon  the 
profile,  the  outlet  being  placed  as  low  as  is  permissible.  This 
should  never  be  below  ordinary  high  water  unless  absolutely 
necessary,  and  under  no  consideration  should  it  be  below  or 


134  SEWERAGE. 

even  as  low  as  ordinary  low  water;  or  rather  this  should  be- 
true  for  the  hydraulic  gradient,  although  the  last  few  feet  of 
the  sewer  may  be  given  a  steeper  grade  to  bring  the  outlet 
below  the  water-surface  or  into  the  channel. 

There  may  be  other  lines  also  where  the  surface  elevations 
demand  the  flattest  possible  grades;  that  is,  the  grades  which 
will  give  the  minimum  permissible  velocity.  This  grade  will 
depend  upon  the  size  of  the  sewer,  and  this  again  upon 
the  quantity  of  sewage.  To  ascertain  this  size,  reduce  the 
maximum  sewage  flow  to  cubic  feet  per  second,  divide  by  the 
desired  velocity  of  flow  in  feet  per  second,  multiply  the 
quotient  by  1.5  for  mains  or  2  for  laterals,  and  find  the  diam- 
eter of  a  circle  having  this  product  as  its  area,  which  will  be 
the  sewer  diameter  required.  Or,  divide  the  gallons  of 
sewage  per  day  times  1.5  or  2,  as  the  case  may  be,  by  the 
required  velocity  in  feet  per  second,  and  take  the  size  corre- 
sponding to  the  next  highest  quantity  in  the  following  table: 

TABLE  No.  16. 

Sizeofsewer 8"            10"            12"            15" 

Gallons  of  sewage  per  day 225,500    352,500     507,600     792,800 

v 

Sizeofsewer 18"                20"                 24" 

Gallons  of  sewage  per  day 1,141,700      1,410,300       2,030,500 

v 

Where  possible  the  grades  of  house-sewers  should  be  such 
as  to  give  a  velocity  of  from  3  to  4  feet  per  second,  and  those 
of  storm-sewers  from  4  to  5  feet  per  second.  The  demands 
of  economical  construction  and  the  necessity  for  sufficient  fall 
in  house-connections  should  not,  however,  be  sacrificed  to 
reduce  velocities  to  less  than  10  or  12  feet,  which,  however, 
should  be  the  maximum  allowed. 

If  it  is  possible  the  grade  of  the  various  sewers  should  be 
so  proportioned  that  the  velocity  of  the  sewage  shall  increase 
as  the  outlet  is  approached,  or  at  least  it  should  not  decrease,. 


THE  DESIGN.  135 

since  a  decrease  in  velocity  may  cause  a  deposit  of  suspended 
matter.  Frequently,  however,  it  is  impossible  to  attain  this 
in  the  design,  since  the  flattest  surface  slopes  are  usually 
nearest  to  the  outlet,  and  the  sewer  grades  are  largely  con- 
trolled by  these. 

From  the  formulas  Q  =  aV  and  V  —  c  VRS,  considering 
the  sewer  as  flowing  full,  and  giving  c  a  constant  value  of  85, 
which  will  in  no  case  vary  more  than  10$  from  Kutter's  c  for 
pipes  ranging  from  8  to  18  inches  diameter,  we  have  the 
formula 


or 

F=2i.i 

V  being  in  feet  and  Q  in  cubic  feet  per  second.  This  formula 
should  not  be  used  where  any  considerable  accuracy  is 
demanded,  but  will  be  found  convenient  for  use  in  fixing  the 
first  approximate  grades.  If  V  is  to  be  a  constant  .S  must  vary 
inversely  as  VQ. 

S,  however,  equals  j  if  /  equals  the  fall  of  the  grade  for 

a  length  /.  If  /,  /',  I",  etc.,  be  taken  as  the  lengths  between 
successive  manholes,  f,  ff,  /",  etc.,  as  the  corresponding 
falls,  and  Q,  Q',  Q",  etc.,  as  the  quantities  of  sewage  flowing 
through  these  lengths,  then 


also/+/'  +  /"  +  etc.  =  F,  the  total  fall  from  the  head  to 
the  outlet  of  the  system.  Knowing  F,  and  /  and  Q  for  each 
length  between  manholes,  we  can  obtain  the  values  of/,/7, 
f"9  etc.  As  just  stated,  it  is  seldom  that  an  entire  system 
can  be  designed  to  give  a  constant  velocity  to  the  sewage, 


136  SEWERAGE. 

but  this  is  sometimes  possible  in  separate  drainage-areas,  a 
constant  velocity  being  obtained  in  each  area. 

Still  more  important  than  obtaining  a  constant  or  con- 
stantly increasing  velocity  is  the  keeping  of  the  velocity  within 
the  limits  given  in  Art.  22.  If  the  ground-surface  is  too  flat 
to  permit  of  obtaining  this  velocity  by  gravity  pumping  must 
be  resorted  to  (see  Art.  42).  If  the  surface  is  steeper  than  is 
permissible  for  the  sewer  the  sewer  grades  can  be  broken  and 
a  drop  made  at  each  manhole  (see  Art.  41). 

A  slight  drop  in  the  grade  should  be  made  at  each  man- 
hole on  flat  grades  to  compensate  for  the  obstruction  offered 
by  curves,  etc.,  at  this  point,  and  for  slight  errors  in  measure- 
ment. 0.02  or  0.03  feet  is  usually  sufficient. 

Of  the  above  principles  the  most  important  is  that  the 
velocity  of  the  sewage  shall  be  within  the  proper  limits;  then 
that  all  basements  and  cellars  to  a  reasonable  depth  shall  be 
drained  by  house-sewers;  also  the  depth  of  excavation  should 
be  kept  as  light  as  possible,  and  the  principles  outlined  in 
Art.  34  should  be  regarded.  The  obtaining  of  the  nearest 
possible  approach  to  an  ideal  design  will  usually  require  many 
changes  in,  and  rearrangement  of,  both  lines  and  grades,  since 
a  change  in  those  of  one  lateral  may  in  some  way  affect  the 
entire  system. 

The  preliminary  grades  having  been  thus  fixed  according 
to  the  desirable  depths  and  velocities  of  flow,  the  size  of  the 
sewer  for  each  reach  should  be  calculated  or  taken  from  the 
diagram  and  the  velocities  checked  by  accurate  calculation. 
Additional  changes,  usually  slight,  will  probably  be  required 
to  obtain  the  best  values  for  each  interdependent  velocity, 
size,  and  depth.  The  junctions  and  crossings  of  the  sewer-lines 
must  be  carefully  examined  and  adapted  to  each  other.  It  is 
a  good  plan  to  make  a  list  of  all  the  manholes,  showing  for 
each  the  elevation  at  which  each  sewer  enters  and  leaves  it. 
Two  sewer-lines  should  never  intersect  each  other,  each 


THE   DESIGN.  1 37 

having  a  continuous  grade;  either  one  should  discharge  from 
both  directions  into  the  other  or  they  should  cross,  the  one 
above  the  other. 

At  junctions  the  surface  of  the  sewage  in  the  contributing 
sewer  should  never  be  designed  to  be  lower  than  that  in  the 
other;  that  is,  if  they  are  both  branch  sewers  the  centre  of 
the  tributary  should  not  be  below  the  centre  of  the  intercept- 
ing sewer;  if  the  larger  is  a  main  the  centre  of  the  smaller 
should  not  be  lower  than  a  point  two  thirds  the  diameter  of 
the  larger  above  its  invert.  It  would  be  still  better  to  place 
the  invert  of  the  tributary  above  the  sewage-surface  in  the 
interceptor,  particularly  when  the  former  drains  but  a  small 
district;  but  where  the  total  fall  possible  is  slight  none  of  it 
need  be  utilized  for  this  purpose. 

Difficulty  will  sometimes  be  found  in  so  arranging  the 
comparative  depths  of  storm-  and  house-sewers  that  the 
house-connections  can  pass  under  or  over  the  former.  In 
some  cases  this  may  be  impossible,  and  it  may  be  necessary 
to  place  a  house-sewer  on  each  side  of  the  storm-sewer. 

Reference  to  the  data  of  locations  and  depths  of  gas-  and 
water-pipes  and  other  existing  sub-surface  systems  should  be 
constantly  made  and  the  sewers  so  designed  as  to  interfere 
with  them  as  little  as  possible. 

On  the  profile  of  each  sewer-line  the  elevation  of  all  trans- 
verse sewers  should  be  indicated  and  a  cross-section  of  the 
sewer  shown.  On  the  finished  profile  it  is  well  to  indicate 
the  thickness  and  material  of  the  sewer-walls  and  of  all  man- 
holes, lamp-holes,  and  other  appurtenances.  The  materials 
may  be  indicated  by  colors,  as  red  for  brick,  brown  for  sewer- 
pipe,  etc.  The  grade,  length,  and  size  of  the  sewer  between 
each  two  manholes  should  be  given  in  figures,  as  well  as  the 
exact  elevation  of  the  invert  at  each  change  of  grade. 


138  SEWERAGE. 


ART.  38.     INVERTED  SIPHONS. 

Since  the  ordinary  sewer  is  designed  to  flow  only  J  to  f 
full,  while  an  inverted  siphon,  being  under  a  head,  will  flow 
full  bore,  the  velocity  in  the  latter  will  be  only  \  to  f  that  in 
the  sewer  laid  to  the  hydraulic  gradient,  if  they  are  of  the 
same  size.  On  account  of  the  difficulty  of  access  and  repairs 
it  is  especially  necessary  that  the  velocity  of  flow  in  the  siphon 
should  be  at  least  as  great  as  that  in  the  ordinary  sewer,  that 
deposits  may  be  prevented.  This  can  be  attained  only  by 
reducing  the  size  of  the  siphon-pipe.  Moreover,  this  velocity 
should  be  had  from  the  beginning  of  the  use  of  the  system; 
and  therefore  this  size  should  be  designed  to  give  sufficient 
velocity  to  the  sewage  from  the  first.  This  first  sewage  flow 
may  be  doubled  or  trebled  as  time  passes,  and  the  increase 
may  then  be  provided  for  either  by  giving  sufficient  fall  to  the 
siphon  originally  to  produce  the  greater  velocity  necessary  or 
by  additional  siphon-pipes.  Usually  at  least  two  siphon- 
pipes  are  laid  at  the  first,  that  while  one  is  being  emptied 
and  cleaned  the  other  may  be  used.  The  friction-head  in  the 
inverted  siphon  will  be  greater  than  if  the  sewer  were  laid  to 
the  hydraulic  gradient,  and  consequently  the  gradient  must 
be  steeper.  The  difference  in  elevation  of  the  two  ends  of 
the  siphon  should  be  equal  to  the  fall  required  by  a  sewer  of 
the  same  size  flowing  full  and  of  the  length  of  the  entire 
siphon  (which  is  not  the  horizontal  distance  between  its  ends) 
to  pass  the  given  amount  of  sewage. 

The  velocity  of  flow  in  an  inverted  siphon  is  entirely  inde- 
pendent of  the  fall  therein,  but  depends  upon  the  quantity 
of  sewage,  since  all  of  this  must,  but  no  more  can,  pass 
through  it.  If  the  fall  in  the  inverted  siphon  is  not  sufficient 
the  sewage  will  back  up  the  sewer  until  sufficient  head  is 
obtained  to  produce  the  required  velocity.  Hence  to  prevent 


7*HE   DESIGN.  139 

this  the  fall  in  the  siphon  itself  should  be  made  great  enough 
to  create  the  velocity  which  will  be  required  by  the  largest 
quantity  to  be  passed  at  any  time. 

An  inverted  siphon  may  at  times  be  necessary  for  passing 
under  some  obstruction  in  the  street — as  a  large  conduit  of 
one  kind  or  another,  but  this  should  be  avoided  where 
possible. 

For  details  of  inverted-siphon  construction  see  Articles  49 
and  77. 

ART.  39.     SUB-DRAINS. 

Very  frequently  storm-sewers  are  placed  at  such  a  short 
distance  from  the  surface  that  they  cannot  be  utilized  for 
draining  damp  cellars,  particularly  since  a  cellar  should  be 
connected  with  no  sewer  whose  crown  is  above  its  level,  from 
danger  of  back-water  when  the  storm-sewer  flows  full. 
Ordinarily  the  house-sewer  is  below  the  cellar-level;  but  this 
should  not  be  utilized  as  a  drain,  both  because  the  amount  of 
sewage  may  thus  be  too  largely  increased ;  and  still  more  on 
account  of  the  danger  from  sewer-air,  which  would  have  free 
access  through  the  drain  should  the  trap-seal  evaporate  during 
a  drought,  which  it  is  very  apt  to  do,  and  from  the  cellar  this 
air  might  permeate  the  entire  house. 

From  a  sanitary  point  of  view  the  drainage  of  wet  soils 
is  almost,  if  not  quite,  as  important  as  the  sewerage  and 
should  not  be  neglected.  The  mere  opening  of  sewer-trenches 
tends  to  drain  the  soil,  even  after  they  are  refilled.  But  in 
many  cases  it  is  extremely  desirable  to  provide  other  and 
more  positive  drainage. 

It  is  almost  impossible  to  make  a  perfectly  tight  sewer 
without  great  expense,  and  when  laid  in  wet  ground  sewer- 
joints  may  admit  in  the  aggregate  large  quantities  of  water. 
This  could  be  prevented  and  the  land  adjacent  drained,  to  its 


140  SEWERAGE. 

great  improvement  and  the  health  of  residents  thereon,  if  this 
ground-water  could  be  lowered  along  the  trench  by  some 
means. 

During  construction  in  wet  ground  much  trouble  will  be 
experienced,  even  when  the  pumping  facilities  are  ample,  by 
water  rising  and  flowing  over  newly  laid  inverts,  to  their  per- 
manent injury  (see  Arts.  75  and  76). 

These  difficulties  can  each  and  all  be  met  in  most  cases 
by  the  use  of  sub-drains — that  is,  drains  laid  a  little  below  the 
sewers.  These  are  ordinarily  laid  in  a  narrow  trench  in  the 
bottom  of,  and  at  one  side  or  in  the  centre  of,  the  sewer- 
trench.  Their  use  for  construction  drainage  will  be  consid- 
ered in  Part  II.  When  properly  designed  for  this  purpose 
their  size  will  in  most  cases  be  sufficient  for  the  continuous 
drainage  of  the  land  and  also  for  cellar-drainage.  The  in- 
stances will  be  very  few,  however,  in  which  any  approach  to 
an  accurate  estimate  can  be  made  of  the  amount  of  sub- 
drainage  which  will  be  required  in  a  system.  But  provision 
should  always  be  made  for  sub-drainage  wherever  the  soil  is 
wet,  for  permanent  drainage  if  for  no  other  purpose. 

The  water  flowing  into  such  drains  must  have  some  outlet, 
and  the  most  natural  course  would  be,  when  the  sewage  is 
disposed  of  by  dilution,  to  place  the  outlets  of  sewers  and 
sub-drains  at  the  same  point.  It  may  happen,  however,  that 
the  necessity  for  sub-drains  is  not  foreseen  when  the  sewer- 
outlet  is  being  built;  or  the  place  where  they  will  be  neces- 
sary may  be  so  far  from  this  outlet  that  a  great  length  of 
otherwise  useless  drain-pipe  must  be  laid  to  reach  it ;  also  the 
amount  of  ground-water  may  be  so  much  greater  than  was 
anticipated,  in  spite  of  all  investigations,  that  the  drain-pipe 
near  the  outlet  will  not  carry  it  all.  In  any  of  these  cases 
another  outlet  may  be  desirable  or  necessary.  This  can  fre- 
quently be  found  by  leading  the  sub-drain  in  a  special  trench 
to  a  near  storm-sewer  or  natural  watercourse.  In  some 


OF   THK 

UNIVERSITY 
THE  DESIGN. 

cases,  however,  special  means  must  be  resorted  to,  such  as 
one  of  the  methods  of  pumping  (see  Art.  42). 

If  the  sub-drain  is  necessary  for  construction  purposes  only 
it  may  be  led  to  a  sump-well  where  a  pump  "is  stationed,  and 
broken  and  sealed  at  several  points  after  construction  is  com- 
pleted. (This  last  will  be  necessary,  as  otherwise  the  drain 
would  continue  to  lead  the  ground-water  to  this  point,  which 
might  become  permanently  and  dangerously  water-soaked.) 

Although  the  sub-drain  is  in  most  cases  smaller  than  the 
sewer,  it  must  be  laid  at  practically  the  same  grade.  The 
objection  to  flat  grades  in  house-sewers  does  not  apply  to 
these  so  urgently,  however,  since  the  water  flowing  through 
them,  after  construction  is  completed  at  least,  is  usually  free 
from  suspended  matter  likely  to  cause  deposits.  The  size  and 
position,  then,  are  the  only  elements  of  the  general  design  to 
be  decided  upon.  The  size  it  will  not  be  advisable  to  make 
less  than  6  inches  at  the  outlet  or  for  long  stretches,  but  for 
stretches  of  a  few  hundred  feet  only  and  through  ground  but 
moderately  wet  4-  or  even  2-inch  pipe  may  be  used.  Pipe 
larger  than  10  or  12  inches  is  seldom  used  in  any  but  excep- 
tional cases.  If  a  larger  would  be  required  (and  instances  can 
be  named  where  the  sub-drainage  from  a  small  town  would 
more  than  fill  a  36-inch  pipe)  special  methods  may  be  em- 
ployed ;  such  as  dividing  the  sub-drainage  system  into  small 
sub-systems,  each  having  its  own  outlet,  which  may,  when 
constructed  under  a  storm-sewer,  discharge  into  the  sewer 
immediately  above  it  or  which  may  be  at  a  near  water- 
course. 


ART.  40.     HOUSE-  AND  INLET-CONNECTIONS. 

The  connections  between  the  sewers  and  opposite  houses 
and  storm-water  inlets  are  of  an  importance  second  only  to  the 
sewer-mains.  Any  defect  in  one  of  the  connections,  while 


i42  SEWERAGE. 

limited  in  the  range  of  its  effect,  is  fully  as  detrimental  within 
that  range  to  the  proper  working  of  the  system  as  a  defect 
in  the  main  itself.  Since  the  house-connections  are  subject 
to  extreme  fluctuations  of  discharge  and  hence  to  stoppages, 
as  also  to  the  formation  of  grease  deposits,  it  is  desirable  that 
they  be  equally  as  accessible  as  sewer-mains  for  both  inspec- 
tion and  cleaning,  and  also  that  their  grade  and  alignment  be 
given  equal  care  in  both  the  design  and  the  construction. 
They  should,  if  possible,  be  given  a  uniform  grade  of  not  less 
than  2j#.  Where  the  house  sits  back  from  the  street  an 
observation-hole  (see  Art.  47)  should  be  placed  at  the  fence- 
line,  and  one  should  be  placed  wherever  there  is  a  change  in 
the  line  or  grade.  There  should  also  be  a  hand-hole  in  the 
pipe  just  after  it  enters  the  cellar.  The  junction  with  the 
sewer  should  be  made  by  means  of  branches,  either  Y  or  T. 
It  should  never  be  made  in  pipe  sewers  by  breaking  a  hole 
into  the  shell  and  inserting  a  pipe.  If  the  sewer  be  larger 
than  20-  to  24-inch  a  T  is  advisable,  both  because  this  offers 
easier  inspection  of  the  house-connection  from  its  lower  end, 
which  inspection  can  be  made  by  a  person  entering  the  sewer, 
and  because  the  branch  can  be  placed  entirely  above  the 
ordinary  level  of  the  sewage,  which  position  it  should  occupy 
when  possible  so  as  to  cause  no  interference  with  the  sewage 
flow.  When  the  sewer  is  too  small  to  admit  a  man,  which 
size  will  also  not  admit  of  raising  the  branch  entirely  above 
the  ordinary  sewage  flow  without  giving  it  too  steep  a  pitch, 
a  Y  branch  is  preferable,  because  this  will  retard  the  flow  less 
than  a  T,  and  because  the  house-sewage  will  enter  the  sewer 
at  a  less  angle  with  its  flow.  The  vertical  angle  which  the 
branch  makes  with  the  horizontal  should  not  ordinarily  ex- 
ceed 45°  in  small  sewers,  because  of  the  interference  with  the 
flow  and  of  the  splashing  caused  by  a  vertical  drop  of  sewage 
into  their  relatively  small  stream,  and  because  of  the  danger 


THE  DESIGN.  1 43 

that  the  weight  of  the  house-connection  may  break  in  the 
crown  of  the  sewer. 

It  is  well  to  so  place  the  branch  in  brick  sewers  that  a 
trickling  discharge  from  it  will  flow  over  the  brick  for  the  least 
possible  distance,  that  deposits  from  such  discharge  may  be 
avoided.  In  the  case  of  combined  sewers  this  would  call  for 
placing  the  branch  but  a  short  distance  above  the  invert,  but 
it  should  be  given  such  a  grade  as  to  bring  it  higher  than  the 
crown  of  the  sewer  when  it  reaches  the  cellar. 

Some  engineers  always  use  T  branches,  more  always  use 
Y  branches,  for  house-connections;  but  the  practice  here 
recommended  seems  to  best  utilize  the  advantages  and  avoid 
the  disadvantages  of  each. 

The  connections  with  inlets  should  never  enter  the  sewer 
at  an  angle  with  its  axis  greater  than  45°,  on  account  of  the 
great  disturbance  to  the  flow  which  would  be  occasioned. 
Where  possible,  and  particularly  in  small  sewer-mains,  a 
manhole  should  be  placed  where  each  connection  enters  the 
sewer  and  the  connection  continued  by  a  curved  invert  in  the 
bottom  of  said  manhole  (see  Plate  VIII,  Fig.  5). 

It  is  difficult  to  calculate  the  proper  size  for  a  storm-water 
connection,  but,  since  there  is  little  disadvantage  in  having  it 
larger  than  is  actually  required,  while  the  effect  of  too  small 
a  pipe  may  be  disastrous,  it  is  advisable  to  make  the  size  fully 
ample  to  discharge  all  the  run-off  from  the  heaviest  storms. 
A  12-inch  pipe  is  probably  the  smallest  which  should  ever  be 
used;  while  a  24-inch  may  be  required  if  the  sewer  lies  near 
the  surface  (thus  giving  little  fall  to  the  connection)  and  if  the 
tributary  area  is  large.  Where  considerable  undeveloped 
territory  drains  into  the  head  of  a  sewer-main,  or  a  small 
stream  is  there  received,  it  may  be  necessary  to  continue  the 
sewer  to  the  inlet,  not  only  not  diminished  in  size  but  even 
enlarged  into  a  bell  mouth.  It  would  be  advisable  to  use  an 


144  SEWERAGE. 

increaser  at  the  upper  end  of  every  inlet-connection,  since, 
owing  to  the  churning  of  the  water  in  the  inlet,  a  "  standard 
orifice  "  will  not  pass  more  than  two  thirds  the  water  which 
can  be  carried  by  a  pipe  of  the  same  size. 

ART.  41.     MANHOLES,  INLETS,  FLUSH-TANKS,  ETC. 

The  necessity  for  frequent  connections  between  the  air  of 
the  sewer  and  the  outer  air  has  been  shown  (Articles  28  and 
29).  As  one  means  for  this,  and  one  which  can  always  be 
adopted,  manholes  should  be  adapted  to  serve  this  end  by 
having  perforated  covers.  For  this  purpose,  also,  the  more 
numerous  they  are  the  better.  The  other  and  greater  neces- 
sity for  their  use,  that  of  providing  access  to  the  sewers, 
should,  however,  have  greater  weight  in  fixing  the  distances 
which  should  separate  them.  It  has  been  found  in  practice 
that  a  6-  or  8-inch  sewer  can  be  easily  inspected  and  cleaned 
if  this  distance  be  not  greater  than  300  feet;  a  12-  or  i8-inch 
sewer,  when  not  more  than  400  feet  separates  successive  man- 
holes. A  sewer  which  can  be  entered  may,  for  this  purpose, 
have  its  manholes  even  600  or  1000  feet  apart;  but  the  cost 
and  difficulty  of  cleaning  are  thereby  increased,  owing  to  the 
distance  the  material  removed  in  cleaning  must  be  carried 
through  the  sewer.  Ventilation  also  is  not  so  well  served  by 
so  great  intervals.  It  is  better  to  fix  500  or  600  feet  as  the 
maximum  distance  between  manholes  on  lines  of  the  largest 
sewers. 

Economy  would  suggest  placing  a  manhole  at  each  sewer 
intersection,  where  it  would  serve  both  lines.  This  is  also 
desirable  as  permitting  a  curved  junction  between  the  sewer- 
channels.  Where  a  curved  bend  is  made  in  the  entire  sewer 
a  manhole  should  be  placed  at  each  end  of  the  curve  unless 
the  sewer  is  sufficiently  large  to  be  entered. 

A  manhole  should  be  placed,  in  general,  at  each  change 


THE   DESIGN.  145 

of  line  or  grade,  in  order  that  every  part  of  the  sewer  may  be 
easily  inspected. 

Economy  will  set  a  limit  to  the  number  of  manholes  which 
may  be  introduced;  the  number  of  the  breaks  in  the  street- 
paving  caused  by  their  covers  it  is  also  desirable  to  keep  at  a 
minimum.  Principally  for  the  first  reason  a  manhole  is  some- 
times omitted  in  small  sewers  when  it  would  come  less  than 
200  feet  distant  each  way  from  another  manhole,  and  a  lamp- 
hole  substituted.  While  the  sewer  cannot  be  inspected  from 
this,  a  light  can  here  be  lowered  into  it  to  light  up  the  sewer 
for  inspection  from  the  next  manhole  either  way.  Also  a. 
hose  can  be  inserted  at  a  lamp-hole  for  cleaning  the  sewer. 

The  use  of  flush-tanks  has  already  been  discussed  (Articles-. 
25-27).  The  grades  of  the  laterals  and  the  conditions  of  their 
use  should  be  carefully  examined  to  determine  where  fre- 
quent flushing  will  probably  be  needed.  In  some  cases,  such 
as  where  a  flat  grade  on  a  long  line  of  small  sewer  is  unavoid- 
able, it  may  be  desirable  to  place  automatic  flush-tanks  at 
intervals  of  800  to  1000  feet  along  its  length,  the  tanks  being 
placed  at  one  side  of  the  sewer  and  discharging  into  it 
through  a  short  connecting-pipe.  If  automatic  appliances  are 
not  employed  no  special  tanks  need  be  built  in  such  a  case, 
but  manholes  at  intervals  along  the  line  can  be  used  for 
flushing. 

All  the  local  conditions  should  be  examined  that  advan- 
tage may  be  taken  of  any  opportunities  for  flushing  offered 
by  springs,  streams,  or  any  available  sources  of  water,  and  in 
general  decision  made  as  to  the  places  and  methods  of  flush- 
ing, As  a  general  rule  every  dead  end  of  a  house-  or  com- 
bined sewer  should  be  flushed  frequently  and  some  arrange- 
ment for  this  placed  at  each  such  point. 

Inlets  should  be  provided  at  frequent  intervals  throughout 
the  area  drained  to  receive  the  surface-water.  In  districts 
where  the  street  traffic  is  considerable  and  where  any  great 


146  SEWERAGE. 

depth  of  water  in  the  gutters  would  inconvenience  a  large 
proportion  of  the  population  the  inlets  should  be  not  more 
than  200  or  300  feet  apart,  while  in  residence  districts  they 
may  be  so  situated  as  to  require  the  run-off  to  flow  for  600  or 
700  feet  over  the  surface.  They  should  generally  be  so 
placed  that  all  the  run-off  can  reach  them  by  flowing  along 
the  gutters  only,  and  need  not  flow  across  the  streets.  The 
plan  Plate  V  shows  how  this  can  be  accomplished  in  most 
cases.  Where  this  is  impossible  a  culvert  should  be  placed 
under  the  street-pavement  in  line  with  the  gutter. 

Where  street  grades  are  continuous  from  one  intersecting 
street  to  another  inlets  should  be  placed  on  street-corners. 
They  are  frequently  placed  at  the  gutter  intersection ;  but  a 
better  plan  in  many  cases,  particularly  on  steep  grades,  is  to 
place  two  openings,  one  just  above  each  cross-walk,  as  this 
avoids  the  vehicle-trap  caused  by  the  ordinary  corner  inlet. 
Also  an  inlet  should  be  placed  at  every  point  where  two  falling 
grades  meet,  and  if  this  be  between  street  intersections  an 
inlet  must  be  placed  there  on  each  side  of  the  street. 

In  the  majority  of  cities  a  large  proportion  of  the  inlets 
are  provided  with  catch-basins — more  than  the  best  practice 
would  warrant,  in  the  author's  opinion.  The  object  of  using 
a  catch-basin  is  to  retain  there  the  silt  and  other  heavy  matter 
and  not  permit  it  to  be  carried  into  and  deposited  in  the 
sewer.  Catch-basins  should  be  cleaned  after  every  storm. 

The  objection  to  catch-basins  is  that  several  days  some- 
times must  elapse — and  several  weeks  usually  do — between 
the  beginning  of  a  storm  and  the  cleaning  of  the  catch-basin; 
and  during  this  time  the  organic  matter  which  has  been 
washed  or  thrown  into  the  inlet,  including  horse-droppings, 
fruit  and  vegetable  refuse,  etc.,  is  putrefying  and  frequently 
emitting  objectionable  odors.  "  Such  foulness  is  less  offensive 
in  the  drains  [storm-sewers]  than  in  the  catch-basins,  which 
are  situated  at  the  sidewalks  and  where  it  is  much  more 


THE  DESIGN.  147 

likely  to  be  observed.  Also  it  is  found  impracticable  to 
intercept  all  matter  in  the  catch-basins  which  would  deposit 
in  the  drains  after  they  reach  the  flat  grades  in  the  lower  part 
of  your  city.  The  cleaning  of  the  drains  would,  therefore, 
be  necessary  in  any  event,  and  the  additional  amount  of  silt 
that  would  be  intercepted  by  the  .catch-basins  will  not  cost 
much  more  to  remove.  In  the  city  of  Paris,  even  though  a 
combined  system  of  sewers  is  used,  it  is  not  found  objection- 
able to  allow  all  the  street-dirt  to  enter  the  sewers  and  there- 
fore the  catch-basins  at  the  inlets  are  omitted."  (Report  of 
Rudolph  Hering  and  Samuel  M.  Gray  on  Sewerage  of  Balti- 
more.) 

As  a  matter  of  fact  catch-basins  are  not  infrequently  left 
uncleaned  after  light  storms,  or  even  heavy  ones,  for  weeks 
together,  and  the  odors  from  them  are  usually  attributed  to 
the  sewers,  which  in  most  cases  are  far  less  foul.  Moreover, 
catch-basins  are  usually  cleaned  with  shovels  only  and  suffi- 
cient filth  left  upon  the  sides  and  bottom  to  become  noticeable 
by  its  odors.  When  cleaned  so  infrequently  the  catch-basin 
often  stands  full  of  material  and  is  until  cleaned  practically 
non-existent  so  far  as  any  useful  effect  is  concerned. 

For  these  reasons  the  universal  use  of  catch-basins  is,  in 
the  author's  opinion,  not  to  be  advised,  but  rather  the  inlet 
should  be  so  designed  that  all  material  shall  at  once  reach  the 
sewer.  The  inlet-connection  he  would  also  make  without  a 
trap,  that  it  may  assist  in  the  ventilation  of  the  sewer;  and  if 
the  sewer  and  its  appurtenances  are  properly  designed,  con- 
structed, and  maintained  there  will  be  very  few  instances 
where  any  odor  can  be  detected  at  the  inlet. 

There  may  well  be  cases  where  catch-basins  are  desirable, 
as  where  the  wash  from  a  steep  hillside  is  caught,  or  for  other 
reason  a  large  amount  of  coarse  soil  or  "  clean  dirt  "  finds  its 
way  to  the  inlet ;  and  there  the  catch-basin  will  need  to  be 
large,  that  but  a  small  proportion  of  this  may  reach  the  sewer, 


148  SEWERAGE. 

and  should  be  cleaned  after  every  heavy  shower.     A  small 
catch- basin  is  in  most  locations  worse  than  useless. 

Catch-basins  are  also  desirable  where  the  sewer  grades  are 
very  flat  and  the  velocity  is  less  than  3  feet  per  second ;  also 
on  combined  sewers  where  the  streets  are  unpaved. 

ART.  42.     PUMPING  OF  SEWAGE. 

There  will  frequently  occur  instances  where,  even  if  the 
sewers  be  laid  at  the  flattest  permissible  grades,  either  the 
outlet  will  come  too  low,  or  the  upper  ends  or  some  inter- 
mediate point  will  be  too  high  for  proper  service.  This  is 
especially  likely  to  occur  where  the  outlet  is  at  a  considerable 
distance  from  the  city ;  also  where  treatment  of  the  sewage  is 
necessary.  Under  such  circumstances  there  is  but  one  solu- 
tion of  the  difficulty — the  sewage  must  be  raised  at  some  one 
or  more  points  from  a  low  to  a  higher  level.  (Where  a  street 
has  not  yet  been  graded  or  built  upon  it  may  often  be  prac- 
ticable to  lay  the  sewer  above  the  ground-surface  in  crossing 
a  valley  or  basin,  and  so  grade  the  street  finally  as  to  give  it  a 
proper  covering,  thus  avoiding  the  necessity  of  pumping.) 

Where  the  sewage  is  discharged  into  tidal  waters  and  the 
outlet  is  below  high  tide  the  lower  stretch  of  the  sewer  will 
be  filled  twice  a  day,  and  the  velocity  therein  cannot  then 
exceed  the  quotient  obtained  by  dividing  the  volume  of 
sewage  by  the  area  of  the  sewer.  It  would  therefore  be  well 
to  make  this  sufficiently  large  for  present  needs  only  and 
duplicate  it  when  greater  capacity  becomes  necessary.  In 
some  instances  tidal  basins  are  constructed,  which  are  closed 
— automatically  in  most  cases — against  the  rising  tide,  and 
receive  and  hold  the  sewage  flow  during  high  tide,  their  con- 
tents being  discharged  on  the  falling  of  the  tide.  In  some 
cases  the  sewers  themselves  are  made  sufficiently  large  near 
the  outlet  to  serve  as  reservoirs  in  the  same  way»  But  these 


THE   DESIGN.  149 

reservoirs  are  seldom  satisfactory,  owing  largely  to  the  diffi- 
culty of  cleansing  them  from  the  deposits  made  while  they  are 
filled  with  stagnant  sewage.  It  would  be  better,  though  of 
course  more  expensive,  to  pump  the  sewage  during  high  tide; 
or  better  still  to  raise  the  streets  and  sewers  generally,  where 
this  is  possible,  and  discharge  above  high  tide.  (The  city  of 
Chicago  some  years  ago  raised  the  streets  over  its  entire  area 
to  permit  of  better  drainage.) 

In  certain  places  the  conditions  are  such  that  the  water 
rises  above  the  sewer-outlet,  which  is  ordinarily  free,  for 
periods  of  days  or  even  weeks;  as  on  a  lee  shore  during  a 
storm  or  on  rivers  subject  to  extended  floods.  In  such  a 
case  pumping  is  necessary;  but  the  first  cost  of  the  plant 
should  be  kept  at  a  minimum,  since  the  interest  on  this  will 
far  exceed  any  saving  that  could  be  made  in  running-expenses 
for  a  few  days.  If  possible  it  is  well  to  locate  the  plant  where 
power  can  be  obtained  from  an  outside  source — as  steam  from 
the  boilers  of  a  water-works  pumping-plant,  electricity  from  a 
power  or  traction  company,  etc. — by  which  means  both  first 
•cost  and  running-expenses  may  be  reduced. 

Where  house-sewage  only  is  to  be  raised  the  apparatus 
should  be  of  a  capacity  sufficient  for  the  maximum  flow. 
Storm-sewage,  or  at  least  the  entire  run-off  from  heavy 
storms,  is  not  often  pumped,  owing  to  the  enormous  capacity 
required  in  the  machinery.  It  will  in  most  cases  be  found 
more  economical  to  build  special  outlets  for  the  storm-sewage 
to  the  nearest  watercourse,  where  this  is  practicable.  In  the 
case  of  a  combined  sewer  the  house-sewage  should  all  be 
pumped,  as  should  even  the  run-off  from  light  storms,  which 
carries  street-washings.  But  it  will  usually  be  permissible  to 
allow  the  run-off  from  heavy  rains  with  the  admixture  of 
house-sewage  to  escape  by  overflows  and  special  storm-sewers 
to  nearer  outlets.  If  this  would  give  rise  to  danger  or  a 
nuisance,  owing  to  even  the  small  proportion  of  house-sewage 


150  SEWERAGE. 

contained,  it  is  probable  that  the  separate  system  should  be 
employed,  all  house-sewage  being  pumped  and  each  storm- 
sewer  seeking  the  nearest  outlet. 

In  a  very  flat  country  it  may  be  desirable  to  raise  the 
sewage  at  a  great  number  of  points  to  prevent  deep  and 
expensive  excavation.  A  sewer  under  a  level  surface,  begin- 
ning at  a  depth  of  8  feet  and  falling  I  foot  in  300,  would  in 
2100  feet  have  a  depth  of  15  feet.  Beyond  this  the  cost  of 
construction  would  rapidly  increase  unless  the  sewage  could 
be  lifted  and  started  again  at  a  depth  of  8  feet. 

Whether  the  lifting  of  the  sewage  shall  be  done  at  one 
station  or  at  several  is  usually  a  question  of  cost  only.  It 
can  be  exactly  settled  only  by  a  comparison  of  the  sum  of  the 
interest  on  first  cost  and  the  operating-expenses  of  one 
method  as  compared  with  another.  (It  is  assumed  that  the 
depth  of  every  sewer  is  made  sufficient  to  meet  all  require- 
ments.) The  fewer  the  lifting-stations  and  the  further  apart 
they  are  the  greater  will  be  each  lift ;  also  the  greater  will  be 
the  average  depth  of  sewer.  Hence,  while  the  greater  the 
distance  between  lifts  the  less  will  be  the  total  cost  of  lifting 
machinery  or  apparatus,  and  also  of  maintenance  of  the  same; 
on  the  other  hand  the  greater  will  be  the  cost  of  the  construc- 
tion of  the  sewer  and  also  of  its  maintenance.  The  proper 
decision  as  to  the  number  and  location  of  the  lifting-stations 
is  frequently  a  problem  requiring  much  careful  study.  While 
in  one  locality,  where  excavation  is  expensive,  5  feet  may  be 
the  maximum  lift  which  will  be  economical,  in  another  this 
limit  may  reach  30  feet  or  more.  If  all  the  lifting  can  be 
done  at  one  or  two  points  it  is  usually  most  economical  to  so 
arrange  it,  even  at  great  expense  for  excavation. 

The  methods  and  apparatus  to  be  employed  may  be: 
pumping  by  steam,  gas,  gasoline,  or  hot-air  engines  or  electric 
motors,  lifting  by  a  Shone  Ejector,  an  Adams  Sewage-lift, 
or  other  appliance  which  seems  adapted  to  the  circumstances. 


THE  DESIGN.  I$I 

If  steam,  gas,  gasoline,  or  hot  air  be  employed  a  complete 
plant  must  be  placed  at  each  lifting-station.  Where  elec- 
tricity is  the  motive  power  a  motor  and  pump  only  are 
required  at  each  station.  This  renders  possible  a  saving  by 
using  electricity,  under  certain  conditions,  such  as  many  lift- 
stations  with  a  small  horse-power  required  at  each;  or  even 
when  the  horse-power  is  considerable.  For  five  stations  at 
New  Orleans,  of  very  great  pumping  capacity,  B.  M.  Harrod 
estimates  the  annual  cost  as  follows: 

Steam.  Electricity. 

Interest  and  depreciation. .  $42,143  $58,684 

Operation 69,960  5 


Total $112,103  $113,509 

If  the  difference  in  cost  of  real  estate  for  the  two  systems 
be  allowed  for,  the  annual  cost  would  probably  balance  very 
closely.* 

The  pumps  usually  employed  are  the  piston-  or  plunger- 
pump  and  the  centrifugal  pump.  Other  devices  have  been 
employed,  such  as  screw  and  oscillating  pumps,  but  few  with 
any  success.  The  centrifugal  pump  requires  a  quite  constant 
volume  of  sewage  for  its  proper  working;  hence,  usually,  a 
storage-basin,  which  is  objectionable.  For  low  lifts,  however, 
it  is  frequently  more  economical  than  a  piston-pump;  also  the 
wear  due  to  grit  in  the  sewage  is  neither  so  great  nor  so 
injurious  to  the  pump,  and  hence  the  necessity  for  screening 
the  sewage  is  not  so  great  as  with  the  piston-pump.  With 
the  latter  particularly  care  should  be  taken  to  remove  all  large 
solids  and  gritty  matter.  For  this  purpose  gratings,  wire 
screens,  and  settling-tanks  are  employed,  the  last  being  of 
such  cross-section  that  the  velocity  through  them  is  less  than 
one  foot  per  second.  These  should  be  near  or  in  the  pump- 

*  Since  the  above  was  written  electric  pumping  has  been  adopted  for 
this  work. 


152  SEWERAGE. 

ing-station  in  order  that  they  may  be  under  the  inspection  of 
the  engineer  and  that  the  deposits  may  be  raised  to  the 
surface  by  power.  If  a  steam-plant  is  used  the  screenings 
can  be  burned  on  specially  prepared  grates. 

The  Shone  Ejector  is  a  device  for  raising  sewage  which  is 
actuated  by  compressed  air.  It  is  usually  employed  where  a 
number  of  lifting-stations  are  needed,  and  the  compressed  air 
for  all  is  supplied  through  iron  pipes  from  one  air-compressing 
station.  While  the  prime  motive  power,  steam,  is  employed 
indirectly,  the  efficiency  of  compressor,  air-pipe,  and  ejector 
combined  is  greater  than  if  a  number  of  separate  steam- 
pumps  are  used,  with  either  separate  boilers  or  a  central  steam- 
plant,  especially  when  the  stations  are  numerous  and  widely 
scattered.  For  only  two  or  three  stations  the  economy  of 
their  use  is  doubtful. 

At  Margate,  England,  sewage-lifts  are  used,  with  city 
water  under  considerable  pressure  as  a  motive  power. 

At  Aberdeen,  S.  Dak.,  two  Worthington  motors  con- 
nected with  a  sewage-pump  are  driven  directly  by  pressure 
of  the  water  from  an  artesian  well.  The  capacity  is  3,500,000 
gallons  per  day,  lifted  23  feet. 

The  Adams  Sewage-lift  can  be  employed  where  the  sur- 
face grade  at  some  part  of  the  system  will  admit  of  introduc- 
ing a  drop,  either  vertical  or  on  a  steep  grade  through  a  pipe 
under  pressure,  in  the  line  of  some  sewer  or  sewers.  The 
sewage  in  making  this  drop  transfers  its  energy  by  the 
medium  of  compressed  air  through  pipes  to  a  lift-station. 
The  more  frequent  application  of  the  Adams  lift,  however,  is 
in  flat  districts  where  city  water  is  usually  employed  for  com- 
pressing the  air,  the  supply  being  controlled  by  a  ball  cock  in 
a  catch-basin  at  the  lift-station. 

From  none  of  these  lifting  appliances  is  there  any  odor, 
under  good  management.  They  can  therefore  be  placed  at 
any  convenient  point.  The  small  pumping-plants,  the  Shone 


THE  DESIGN. 

Ejector  and  Adams  Lift,  are  usually  placed  in  vaults  beneath 
the  surface,  the  larger  plants  above  ground.'  The  sewage- 
pumping  stations  of  London  and  Berlin  are  within  the  city 
limits,  no  odor  whatever  being  perceptible  near  them. 

ART.  43.     INTERCEPTING- SEWERS  AND  OVERFLOWS. 

It  often  happens  that  a  town  lies  in  a  valley  and  upon  the 
slope  on  one  or  both  of  its  sides,  and  that  while  the  valley 
district  is  too  low  to  sewer  to  the  outlet  by  gravity  the  upper 
districts  are  sufficiently  elevated  to  do  so.  In  such  a  case  it 
would  be  useless  to  carry  all  the  sewage  to  a  main  lying  in 
the  valley  and  raise  it  all  to  a  gravity  outlet-line.  Instead 
a  gravity-main  should  be  run  up  each  side  of  the  valley  at  the 
minimum  grade  to  receive  all  the  sewage  from  higher  up  the 
hill,  leaving  only  the  sewage  from  below  this  to  be  pumped. 
Such  a  main  is  called  an  intercepting-sewer. 

In  some  instances  a  combined  sewer  is  provided  with  an 
outlet  to  the  nearest  watercourse,  which  is  for  storm-sewage 
only,  it  being  intended  that  the  house-sewage  shall  be  received 
and  conducted  away  by  another  sewer,  which  also  is  called  an 
intercepting-sewer. 

This  term  is  also  applied  to  a  long  sewer  which  passes 
down  a  valley  and  receives  the  sewage  from  several  systems 
or  parts  of  systems  to  conduct  it  all  to  a  common  outlet. 

It  is  frequently  advisable,  when  the  gravity-outlet  must 
be  below  high  tide,  to  locate  an  intercepting-sewer  which  can 
discharge  above  all  tidal  influence,  that  the  effect  of  the  seal- 
ing of  the  lower  outlet  may  be  felt  by  only  a  part  of  the 
system,  the  upper  sections  discharging  through  the  free  outlet 
of  the  intercepting-sewer. 

It  sometimes  happens  that  a  system  must  be  extended 
further  in  a  given  direction  than  was  anticipated,  or  that  the 
amount  of  sewage  contributed  by  a  district  becomes  greater 


154  SEWERAGE. 

than  the  sewers  can  carry.  This  can  be  remedied  by  running 
an  intercepting-sewer  across  such  gorged  sewers  at  mid-length, 
intercepting  the  sewage  from  above  and  leaving  the  lower 
lengths  to  carry  only  their  local  sewage. 

Where  storm-water  can  find  near  outlets  from  many  dis- 
tricts to  a  stream  or  other  body  of  water,  at  which  outlets, 
however,  the  house-sewage  should  not  be  discharged,  an 
intercepting-sewer  may  be  run  along  and  near  the  water  to 
intercept  the  house-sewage  and  convey  it  to  a  satisfactory 
outlet  or  to  a  disposal  grounds  or  works.  By  a  construction 
of  the  sewers  called  an  interceptor  (see  Art.  48)  the  house- 
sewage  and  the  run-off  from  light  rains,  which  is  the  filthiest 
of  storm-sewage,  may  be  diverted  to  the  intercepting-sewer, 
while  the  run-off  from  heavy  storms  will  reach  the  nearer 
outlet.  Mechanical  contrivances  for  diverting  the  sewage  are 
also  used  (see  Art.  48). 

Another  method  of  obtaining  similar  results  is  that  of 
putting  storm-overflows  in  the  combined  sewers,  a  special 
storm-sewer  taking  the  overflow  sewage  to  a  convenient  outlet. 
The  overflow  is,  in  general,  an  opening  in  the  sewer  with  its 
bottom  elevated  some  distance  above  the  sewer-invert.  Until 
the  sewage  reaches  the  height  of  this  overflow  it  remains  in 
the  combined  sewer  and  flows  to  its  outlet;  when  the  quantity 
becomes  such  that  the  height  of  sewage  flow  is  greater  than 
this  the  surplus  discharges  through  the  overflow  into  the 
storm-water  outlet.  It  is  usually  so  arranged  that  this  shall 
occur  only. when  the  dilution  of  house-sewage  by  storm-water 
has  reached  the  point  where  the  discharge  of  the  mixture  into 
a  stream  is  free  from  all  danger. 

With  either  of  these  constructions  the  overflow  or  the 
interceptor  should,  if  possible,  be  at  such  an  elevation  that  it 
cannot  be  reached  by  floods  or  tides  backing  up  the  storm- 
water  sewer. 


THE  DESIGN.  155 

ART.  44.     USE  OF  OLD  SEWERS. 

In  many  cities,  before  any  general  sewerage  system  is  con- 
structed or  even  thought  of,  short  conduits,  both  private  and 
public,  have  been  built,  discharging  at  the  point  nearest  to 
hand — usually  a  stream  or  lake.  These  are  often  built  in  the 
crudest  manner,  graded  by  eye,  and  generally  larger  or 
smaller  than  necessary.  In  other  cases  the  sewers  are  well 
built  and  graded  and  of  a  size  adapted  to  remove  the  storm- 
water,  but  the  outlet  is  located  where  house-sewage  should 
not  be  discharged,  or  the  sewer  is  not  sufficiently  deep  to 
permit  of  receiving  all  house-sewage,  or  it  is  a  pipe  sewer  and 
is  not  provided  with  sufficient  branches  for  house-connections. 
Such  sewers  can  frequently  be  incorporated  into  the  proposed 
system,  and  a  saving  made  of  the  cost  and  the  tearing  up  of 
the  streets  avoided.  But  a  thorough  examination  of  them 
should  first  be  made  to  ascertain  which  ones  can  be  so  used 
and  how. 

If  they  are  sufficiently  large  they  should  be  entered  and 
their  condition  learned  as  to  size,  grade,  character  of  work- 
manship, etc.  If  the  brick-work  is  very  rough  it  may  be 
desirable  to  clean  it  and  plaster  it  with  cement  mortar.  It 
may  be  cleaned  by  washing  first  with  dilute  muriatic  acid, 
then  with  a  solution  of  potash,  and  then  with  water. 

No  connection-pipes  should  be  allowed  to  protrude  within 
the  sewer.  If  the  junctions  are  not  well  designed  they  should 
be  torn  out  and  rebuilt.  If  necessary  a  sufficient  number  of 
manholes  should  be  built  to  bring  the  intervals  between  them 
within  the  proper  limits.  If  it  is  desirable  to  use  an  old  cir- 
cular sewer  as  a  combined  sewer  the  invert  can  be  narrowed 
as  shown  in  Plate  VII,  Fig.  7. 

If  the  sewers  are  too  small  to  be  entered  they  should  be 
examined  thoroughly  from  the  manholes  by  means  of  mirrors 
(Art.  68);  pills  (Art.  85)  should  be  passed  through  them  to 


IS  SEWERAGE. 

ascertain  whether  the  bore  is  of  uniform  size  and  clear  of 
deposits.  Their  size,  grade,  elevation,  etc.,  should  be  learned 
by  actual  measurement.  If  they  are  not  laid  in  straight  lines, 
particularly  those  less  than  12  or  15  inches  in  diameter,  it  is 
doubtful  if  they  should  be  used,  unless  manholes  and  lamp- 
holes  can  be  so  judiciously  located  as  to  give  straight  stretches 
of  sewer  between  them. 

If  a  pipe  sewer  is  too  high  for  efficient  service  or  at  too 
flat  a  grade  a  trench  may  be  sunk  along  its  line  and  the  pipe 
taken  up,  cleaned,  and  the  good  ones  relaid  at  a  lower  level 
or  better  grade  in  the  same  trench.  In  the  majority  of  cases 
this  probably  will  be  the  best  disposition  which  can  be  made 
of  old  pipe  sewers. 

Owing  to  the  difference  in  character  and  volume  of  house- 
and  storm-sewage  a  sewer  not  adapted  for  use  as  a  house  or 
combined  sewer  may  often  be  used  as  a  storm-sewer.  It  fre- 
quently happens  that  old  combined  sewers,  or  even  the  larger 
house-sewers,  are  admirably  adapted  to  this  use,  and  a 
separate  system  can  then  be  built  for  the  house-sewage. 

If  an  old  combined  sewer,  or  storm-sewer  modified  into  a 
combined  sewer  as  explained  above,  can  be  used,  except  that 
the  house-sewage  should  be  discharged  at  a  new  and  more 
distant  outlet,  this  sewage  can  be  discharged  through  an 
interceptor,  or  diverted  by  a  mechanical  regulator  into  an 
intercepting  house-sewer,  and  the  old  outlet  used  to  discharge 
the  storm-water  only. 

But  the  efficiency  of  the  system  is  of  greater  moment  than 
small  economies,  or  even  large  ones,  and  should  not  be  sacri- 
ficed to  them. 


CHAPTER  VIII. 
DETAIL   PLANS. 

ART.  45.     THE  SEWER-BARREL. 

SEWERS  have  been  made  of  almost  every  conceivable 
shape  and  the  walls  built  of  all  kinds  of  materials.  A  few 
shapes  and  materials  are  of  almost  universal  applicability, 
others  are  adapted  to  peculiar  circumstances  only,  and  some 
are  freaks  of  invention  adapted  to  no  circumstances. 

The  shape  of  cross-section  is  to  a  certain  extent  controlled 
by  the  material  of  which  the  sewer  is  constructed.  The 
smallest  sewers  cannot  be  advantageously  built  of  brick,  but 
are  usually  composed  of  earthenware  or  metal  pipes  or  of 
concrete.  Earthenware  sewers  are  made  from  2  to  42  inches 
interior  diameter.  They  are  seldom  made  other  than  circular, 
owing  to  the  liability  of  other  shapes  to  become  distorted  in 
burning.  Metal  pipes  are  employed  where  the  sewer  will  be 
under  pressure,  as  in  a  siphon,  or  where  there  is  a  great  deal 
of  ground-water;  also  sometimes  to  better  resist  disturbing 
forces,  as  in  made  or  treacherous  ground  or  outlets  under 
water  or  in  shifting  sands.  The  only  metal  commonly  em- 
ployed is  iron.  Metal  pipes  have  always  been  made  circular, 
although  there  are  none  but  economic  reasons  why  other 
forms  could  not  be  made. 

Concrete  and  cement  sewers  are  made  of  all  sizes  and 
shapes — circular,  egg-shaped,  rectangular,  etc. — the  smaller 
sizes  being  usually  of  cement,  the  larger  of  concrete. 

157 


SEWERAGE. 

Wooden-stave  sewer-pipe  has  been  used  in  the  West,  and 
in  the  East  to  some  extent.  On  the  Los  Angeles  outfall 
sewer  are  34,100  feet  of  36-  and  38-inch  pipe  of  this  descrip- 
tion. The  outlet  sewers  in  New  York  and  Brooklyn  are  many 
of  them  creosoted  wooden-stave  pipe  of  3  or  more  feet 
•diameter. 

For  all  sewers  the  circle  is  the  most  economical  shape,  and 
generally  the  most  desirable,  if  they  are  never  to  run  less  than 
|  full,  except  that  the  use  of  platform  foundations  may 
modify  the  first  statement.  But  if  they  are  to  be  used  as 
combined  sewers  the  egg  shape  is  to  be  preferred,  or  a  form 
similar  to  Plate  VII,  Figs.  2  and  6. 

In  Brooklyn,  N.  Y.,  and  a  few  other  cities  cement  sewer- 
pipe  is  used,  and  in  general  all  sizes  of  this  above  12  inches — 
in  Brooklyn  all  sizes — are  egg-shaped.  Sections  of  this  pipe 
are  shown  in  Plate  VI,  Figs.  I  and  2.  The  flat  base  is  given 
the  pipe  to  prevent  its  rolling  in  the  trench  after  being  placed 
in  position  and  to  strengthen  the  bottom  against  crushing. 

In  the  case  of  large  sewers,  particularly  those  whose 
diameter  exceeds  4  or  5  feet,  it  frequently  becomes  necessary 
to  make  the  width  greater  than  the  height,  because  the  depth 
of  the  invert  is  limited  by  sewer-grade  requirements  and  the 
height  of  the  arch  by  the  street  grade.  A  great  number  of 
shapes  have  been  designed  to  meet  these  conditions.  Some 
of  the  best  are  shown  in  Plate  VI,  Fig.  5,  and  Plate  VII, 
Figs.  9  and  10.  Plate  VII,  Fig.  4,  shows  a  design  for  very 
low  head-room,  but  the  thrust  of  the  arch  is  considerable  and 
the  side  walls  should  be  heavier  than  shown  unless  they  are 
firmly  backed  by  rock  or  solid  earth.  Plate  VIII,  Fig.  I,  is 
a  better  design  to  employ  where  the  head-room  can  be 
slightly  increased. 

The  use  of  steel  beams  for  supporting  the  roof,  with 
vertical  side  walls,  as  shown  in  Plate  VII,  Figs.  9  and  10,  is 
becoming  quite  common,  and  is  probably  the  best  construe- 


DETAIL   PLANS.  159 

tion  for  soft  ground  with  limited  head-room.  Fig.  10  is 
adapted  to  storm-water  only,  or  to  a  flow  of  house-sewage 
never  less  than  15  inches  deep.  The  egg-shaped  sewer  in 
Fig.  9  is  intended  for  the  house-sewage,  the  larger  channels 
for  storm-water. 

Plate  VIII,  Figs.  2  and  3,  show  substitutes  for  egg-shaped 
sewers  where  the  head-room  is  contracted.  In  Fig.  3  the 
semicircular  invert  should  be  sufficiently  deep  to  admit  of 
carrying  the  maximum  house-sewage  flow,  that  the  sloping 
benches  may  not  be  fouled  by  it.  Fig.  2  is  especially  adapted 
to  an  exceedingly  variable  house-sewage  flow,  as  from  a  fac- 
tory district  whose  Sunday  and  holiday  flow  is  inconsiderable. 

Plate  VI,  Figs.  5  and  9,  Plate  VII,  Figs.  4,  5,  and  10, 
and  Plate  VIII,  Fig.  i,  are  best  adapted  to  storm-sewage 
only,  although  they  may  be  used  as  combined-sewer  mains  if 
the  depth  of  the  house-sewage  flow  is  never  less  than  4  to  6 
inches  at  the  shallowest  part,  and  the  velocity  is  then 
sufficient.  Plate  VI,  Figs.  I,  6,  7,  and  8,  are  intended  for 
house-sewage  only.  In  Fig.  7  the  flat  invert  is  permissible 
owing  to  the  constant  depth  of  the  sewage  flow,  which  con- 
sists of  intercepted  house-sewage  from  a  number  of  residence 
suburbs. 

Plate  VI,  Figs.  2  and  3,  Plate  VII,  Figs.  I,  2,  3,  6,  7, 
and  9,  Plate  VIII,  Figs.  2  and  3,  are  intended  to  act  as  com- 
bined sewers.  In  Plate  VII,  Figs.  5  and  6,  the  side  bench  is 
horizontal,  that  it  may  serve  as  a  sidewalk  for  sewer  inspectors 
and  cleaners. 

The  circular  or  egg-shaped  form  demands  for  strength  a 
solid  support  under  its  invert.  Where  the  soil  is  clay  or  firm 
loam,  or  a  mixture  of  these  with  sand  or  gravel,  or  rock  easily 
shaped,  such  a  sewer  may  be  built  with  walls  of  uniform 
thickness,  the  invert  bearing  upon  ground  shaped  to  receive 
it.  If  the  ground  is  not  firm,  however,  or  cannot  be  readily 
shaped,  the  sub-invert  spaces  must  be  filled  with  concrete, 


i6o 


SEWERAGE. 
Plate  VI. 


FIG.  3.      l/v'  FIG.  4. 

N  SOFT  EARTH  IN  FIRM   EARTH 

BRICK    SEWER 


BROOKLYN  STANDARD  SECTIONS 


ICK   IN 
PORTLAND 
CEMENT 


^'        U        Ul 

no.  6. 

INTERCEPTING  Sf£WF.R  AND 
SUB-DRAIN.  BALTIMORE,  MD. 


METROPOLITAN  SEWERS  (BOSTON) 


SPECIAL  SECTION  BENEATH  RAILWAYS 

FIG.  3.  SALT  LAKE  CITY. 

OUTLET  SEWER, 


ROCK 
CAVATIOI* 


FIG.  9.  FIG.  10. 

WEST  SIDE  TRUNK  SEWER,  ROCHESTER. 


DETAIL   PLANS. 


161 


brick,  or  stone  masonry,  as  in  Plate  VI,  Figs.  3,  5,  6,  8, 
and  9.  If  the  arch  is  of  such  dimensions  that  the  horizontal 
thrust  becomes  more  than  the  soil  can  receive  without  yield- 
ing, then  the  side  walls  must  be  designed  to  receive  this 
thrust,  as  in  Plate  VI,  Figs.  5,  6,  8,  and  9.  The  general 
principles  of  arches  apply,  of  course,  to  arched  sewers,  one  of 
the  most  important  being  the  necessity  for  stiffness  of  the 
haunches. 

The  circle,  as  has  been  stated,  is  the  most  economic  shape 
for  a  sewer  when  the  invert  requires  no  backing.  When  this 
is  necessary,  however,  the  circle  becomes  an  expensive  shape, 
and  the  most  economic  is  one  with  vertical  side  walls  and 
bottom  flat  or  conforming  generally  to  the  shape  of  the  trench 
bottom.  This  is  seen  by  an  inspection  of  Plate  VI,  Figs.  6 
and  8,  Plate  VII,  Figs.  4  and  10.  It  is  for  this  reason  that 
most  of  the  flat-bottomed  sewers  are  built.  Permanency  of 
construction  demands  a  covering  for  timber  platforms,  which 
are  liable  to  abrasion  and  also  to  rotting  away.  This  cover- 
ing, forming  the  sewer  bottom,  is  usually  given  a  curved  form, 
as  in  Plate  VI,  Fig.  5,  or  a  sloping  one,  as  in  Plate  VIII, 
Fig.  I,  for  two  reasons:  to  concentrate  small  streams  and 
decrease  deposits,  and  to  give  strength  to  the  bottom  to  resist 
the  upward  pressure  which  will  exist  when  the  soil  is  soft  mud, 
quicksand,  or  similar  material. 

The  materials  of  which  sewers  are  commonly  composed 
are  brick,  stone,  and  concrete  masonry,  cement  and  vitrified 
salt-glazed  pipe,  and,  under  special  conditions,  cast-  or 
wrought-iron  or  steel  pipe. 

Stone  and  brick  masonry  is  usually  built  up  in  cement 
mortar,  and  cement  is  always  used  for  concrete.  The  stone 
masonry  is  usually  rough,  but  compact  and  well-built,  rubble. 
In  arches  brick  is  usually  employed,  as  being  cheaper  and  also 
stronger  unless  the  stone  are  carefully  dressed.  The  interior 
surface  of  the  sewer,  when  this  is  built  of  stone,  is  usually 


1 62 


SEWERAGE. 


Plate  VII. 


FIG.  1.  FIG.  2. 

WASHINGTON  D.C.       STANDARD  SEWERS. 


STONE  MASONRY 

CONCRETE/  FIG.  4.    TIBER  CREEK, (WASHINGTON) 

~  SEWER  IN  1893. 

FIG.  3. 


-3-0!L--^ 


FIG.  5.     OLD  STYLE. 


FIG-.  6.     NEW  STYLE.        FIG.  7.     OLD   LONDON  SEWER. 
PARIS        SEWERS  W.THIMP*OVEDINVERT. 


.     DOUBLE  STORM  CHANNEL  AND  HOUSE  SEWER;  BRUSSELS.         FIG.  8.     OLD  LONDON  "SEWER 
UNDER  RAILWAY  TRACKS.  OF  DEPOSIT." 


ji^'  UINUC.H   rxMiuvvrt 

\     •  3$*CONCRETE  ANO  j  PLASTER 

Dfe  — ~ — 190    s* 


;\A  LJ  LJ 

FIG,  10.      CANAL.  STREET  SEWER;    ST.  PAUL,  MINN. 


DETAIL   PLANS.  163 

lined  with  a  4-inch  ring  of  brick,  because  a  brick  surface  can 
be  more  easily  made  smooth  than  can  stone  masonry  (see 
Plate  VI,  Fig.  9).  If  much  wear  is  anticipated  smooth- 
dressed  granite  or  trap  blocks  are  frequently  used  as  invert- 
lining  (see  Plate  VI,  Fig.  8). 

Where  the  foundation  is  yielding  a  concrete  base  is  fre- 
quently used  under  the  sewer,  as  in  Plate  VI,  Fig.  8,  Plate 
VII,  Fig.  9.  But  if  it  is  soft  a  platform  or  even  piles  should 
be  used  under  the  concrete. 

Sewers  built  entirely  of  concrete  have  been  used  in 
Europe  very  extensively  and  are  coming  into  use  in  this 
country.  In  many  localities  concrete  is  cheaper  than  rubble 
or  brick  masonry.  If  well  made  a  concrete  sewer  is  both 
stronger  and  tighter  than  a  stone  or  brick  one,  and  can  be 
made  more  durable  than  many  kinds  of  stone  or  brick.  The 
wearing-surface  should  be  given  a  smooth  coat  of  rich  Portland- 
cement  mortar  J  inch  to  2  inches  thick,  or  a  lining  of  hard 
brick,  which  is  probably  better  owing  to  the  liability  of 
cement  coatings  to  separate  from  the  body  of  the  concrete 
(see  Plate  VI,  Fig.  6;  Plate  VII,  Figs.  I  and  2). 

If  arches  of  small  radius  are  built  of  brick-work  laid  with 
radial  joints  much  cement  is  used,  the  arch  is  often  weak,  and 
the  inner  surface  a  polygon  in  section  rather  than  a  curve, 
unless  brick  especially  shaped  are  used.  If  laid  well  such 
arches  are  also  expensive  in  labor.  To  meet  these  objections, 
which  apply  particularly  to  inverts  in  egg-shaped  brick  sewers, 
invert-blocks  of  vitrified  clay  have  been  used.  There  are 
objections  to  these,  the  principal  of  which  is  that  a  joint 
entirely  through  the  sewer  is  made,  and  where  the  hydrostatic 
head  is  greatest,  which  is  almost  sure  to  permit  the  leakage  of 
water  into  or  out  of  the  sewer.  They  are  also  rather  expen- 
sive, and  are  but  little  used  now.  A  section  of  such  a  block 
is  shown  in  Plate  VI,  Fig.  n. 

A  better  plan  for  constructing  short-radius  inverts  is  by 


164 


SEWERAGE. 


. 


. 


STEEL  I  BEAM 


STEEL  I  BEAM 


I'BOLT 


FIG.  4. 

WOODEN  OUTLET  SEWER 
NEW  YORK  CITY, 


STEEL  I  BEAM 


BG,7.  JUNCTION  OF  BRICK  SEWEBS. 


SECTION  ON  A-B. 

¥\G.5.  JUNCTION  MANHOLE. 


SECTIONAL  PLAN       £ 

FIG.  6.  JUNCTION  OF  8  FT.  AND  1  1  FT.  SEWERS.. 


FIG    8.  FIG    9. 

HUB  &  SPIGOT  JOINT,  RING  JOINT 


FIG    10.  FIGn11- 

BEVEL  JOINT,  ARCHER    JOINT. 


DETAIL   PLANS.  165 

the  use  of  concrete  or  brick,  lined  on  the  inside  with  vitrified 
sewer-pipe  split  into  thirds,  which  is  approximately  the  arc  of 
the  small  invert-circle  in  the  egg-shaped  sewer.  Such  a  con- 
struction is  shown  in  Plate  VIII,  Fig.  2.  This  construction 
is  also  well  adapted  to  such  sewers  as  are  shown  in  Plate  VII, 
Figs.  2,  6,  and  7,  Plate  VIII,  Fig.  3. 

Whole  vitrified  pipe  are  used  for  lining  to  circular  sewers 
up  to  42  inches  diameter,  when  the  pipe  is  not  used  alone  on 
account  of  the  additional  strength  or  tightness  of  joints 
required. 

There  is  no  fixed  rule  for  the  thickness  of  sewers,  which 
depends  upon  the  shape  and  diameter  of  bore,  the  material, 
the  pressure  received  from  the  surrounding  soil,  and  other 
circumstances.  Brick  sewers  less  than  30  inches  diameter  are 
frequently  made  but  one  ring — 4  inches — thick ;  from  this  up  to 
about  60  inches,  2  rings  or  8  inches  thick;  from  this  up  to  120 
inches,  3  rings  or  12  inches  thick.  This  applies  to  the  arch 
more  particularly,  unless  the  surrounding  ground  is  very  firm, 
when  the  invert  may  be  made  of  equal  thickness,  or  even  8 
inches  thick  only  when  the  arch  is  12  inches  or  more  thick. 
Some  engineers  never  use  less  than  two  rings  of  brick  in  a 
sewer-arch ;  some  use  one  ring  up  to  diameters  of  3  feet  or 
more.  The  latter  may  give  sufficient  strength  against  crush- 
ing, but  is  hardly  stiff  enough  to  resist  distortion  except  under 
unusually  favorable  circumstances. 

The  thickness  of  the  side  walls,  when  these  are  vertical, 
must  be  such  as  to  enable  them  to  withstand  the  pressure  of 
the  soil  without  or  of  the  water  within  the  sewer  when  it  is 
full;  also  to  receive  the  thrust  of  the  top  arch  when  the  soil 
is  not  capable  of  doing  so. 

When  two  sewers  intersect  one  or  both  should  be  curved 
in  the  direction  of  flow  of  the  other.  If  one  or  both  are  small 
the  curve  may  be  made  in  a  manhole  (Plate  VIII,  Fig.  5). 
If  one  is  many  times  larger  than  the  other  the  curve  may  be 


1 66  SEWERAGE. 

omitted,  the  branch  making  an  angle  of  45°  with  the  main 
sewer  at  the  junction.  Where  they  are  each  larger  than  30 
to  36  inches  diameter  the  intersection  should  be  made  by 
bringing  the  two  barrels  gradually  into  one.  This  will  require 
considerable  skill  in  both  design  and  construction  when  the 
tops  and  inverts  are  both  arched.  When  the  top  is  a  girder 
construction  the  plan  is  much  simplified,  and  still  more  so  if 
the  bottom  also  is  flat.  The  crown  of  the  sewer  a  short  dis- 
tance below  the  junction  should  be  as  low  as  that  of  the  lower 
of  the  two  sewers  a  few  feet  above  it.  A  plan  of  a  junction 
of  two  circular  sewers  is  shown  in  Plate  VIII,  Fig.  6.  If  the 
head-room  is  limited  the  plan  shown  in  Fig.  7  may  be  used. 
In  Wilmington,  Del.,  the  junction  of  two  6-foot  and  a 
lO-foot  sewer  forms  a  chamber  which  is  roofed  with  counter- 
groined  arches. 

ART.  46.     PIPE  SEWERS. 

Pipe  is  ordinarily  used  for  sewers  up  to  18  or  24  inches 
diameter.  Above  this  up  to  42  inches  vitrified  clay  pipe  is 
sometimes  used,  but  many  engineers  are  doubtful  of  the 
strength  of  the  larger  sizes  against  crushing.  The  smaller 
sizes  up  to  1 8  or  24  inches,  when  made  of  good  clay  well 
burned,  are  sufficiently  strong  for  ordinary  locations,  although 
the  "  double-strength  "  pipe  (having  a  thickness  of  shell  -fa 
the  diameter)  is  recommended  rather  than  those  of  the  stand- 
ard thickness,  which  is  less  than  -fa  the  diameter  by  a  differ- 
ence which  increases  with  the  diameter.  It  has  so  far  been 
found  impracticable  to  make  good,  sound,  symmetrical  clay 
pipe  with  shells  much  thicker  than  fa  the  diameter.  It  is 
probable  that  if  this  thickness  be  maintained  the  largest  sizes 
of  pipe  are  amply  strong  for  ordinary  circumstances. 

In  many  instances  where  vitrified  clay  pipe  has  been 
crushed  in  the  ground  it  has  been  found  that  this  was  probably 


DETAIL 


167 


due  to  the  fact  that  the  pipe  had  a  bearing  on  the  bottom  at 
only  one  or  two  points  instead  of  along  its  entire  length,  or 
that  stones  or  frozen  earth  were  thrown  upon  it  in  back-filling. 
If  earth  is  well  tamped  under  and  around  a  vitrified  clay  pipe 
it  will  not  usually  collapse,  even  when  broken,  although  it 
may  leak.  Such  pipe  ordinarily  breaks  along  four  lines  —  at 
top,  bottom,  and  each  side  —  into  pieces  of  almost  equal  size. 
For  this  reason  fire-cracks  and  slight  imperfections  which  do 
not  cause  the  rejection  of  a  pipe  should  be  placed  at  a  point 
about  45°  above  the  horizontal  in  laying,  and  not  at  the  top. 
Several  tests  have  been  made  of  the  strength  of  vitrified 
clay  pipe.  In  one  series,  in  which  the  pipe  were  bedded  in 
sand  and  the  load  applied  to  the  entire  length  of  the  top, 

8-inch  pipe  broke  when  the  weight  per  foot  of  length  was  1363  to  2256  pounds 
12     "       "         "         "        "         "        "  "     1227  to  2756       " 

15     "       "         "         "        "         "        "      "     "       "         '•    1261  to  2297       " 
18     "       "         "         "        "         "        "       "      "       "         "     1464102093 

From  similar  tests  made  in  1897  F.  A.  Barbour  of  Boston 


deduced  the  expression  /  = 


which  p  is  the  pressure 


per  lineal  foot  in  pounds  at  the  first  cracking,  t  is  the  thick- 
ness in  inches,  d  is  the  diameter  in  inches,  and  c  =  33,000. 

Tests  made  by  T.  H.  Barnes  on  the  strength  of  1  2-inch 
vitrified  clay  pipe  when  acting  as  a  beam  between  supports  2 
feet  apart  gave  the  following  results: 


Thickness. 

Cracked  at 
(Pounds) 

Broke  at 
(Pounds) 

Equal  to 
(Lbs.  per  Lin.  Ft.) 

Remarks. 

' 

IIOO 

2750 

1880 

Fire-crack 

/ 

2000 
2690 
22  2O 
2110 

2OOO 
2810 
2450 
2535 

1330 
1870 
1630 
1690 

The  exact  amount  of  pressure  brought  to  bear  upon  a 
sewer  by  back-filling  is  uncertain.  For  a  few  feet  of  depth  it 
probably  bears  the  entire  weight  of  the  earth  immediately 
above  it.  With  granular  material  the  proportion  of  pressure 


1 68  SEWERAGE. 

to  weight  of  back-filling  probably  decreases  but  little,  while 
with  other  soils  it  decreases  more  or  less  rapidly  after  the 
depth  equals  the  width  of  the  trench.  But  it  is  probable  that, 
while  the  latter  material  gives  an  almost  vertical  pressure,  the 
former  acts  more  as  a  fluid,  pressing  normally  to  the  surface 
of  the  sewer,  and  is  not  so  liable  to  crush  it.  Little,  however, 
is  known  on  this  point.  From  certain  experiments  in  which 
natural  conditions  were  only  partially  reproduced  it  was 
thought  probable  that  for  trenches  10  feet  or  more  deep  the 
percentage  of  weight  of  back-filling  transmitted  to  the  sewer 
equalled  I  —  coefficient  of  friction  of  the  material;  that  gravel 
transmits  36  per  cent  and  wet  clay  65  per  cent  of  its  weight; 
that  up  to  10  feet  the  percentage  transmitted  decreased  from 
100  per  cent  as  the  square  or  cube  of  the  depth.  If  the 
depth  of  covering  is  small  there  is  danger  that  outside  weight 
from  road-rollers  or  even  heavy  wagons  may  crush  it.  But 
this  danger  appears  to  be  very  slight  when  the  depth  of 
covering  equals  or  somewhat  exceeds  double  the  width  of 
trench. 

The  joints  of  vitrified  clay  pipe  sewers  are  generally  made 
of  the  bell-and-spigot  pattern,  as  shown  in  Plate  VIII, 
Fig.  8.  The  ring-joint  (Fig.  9)  is  not  now  very  extensively 
used,  as  its  supposed  advantages  are  found  to  be  largely 
imaginary,  while  its  disadvantages  are  not.  It  is  almost  im- 
possible to  make  tight  joints  with  the  ordinary  ring-joint  and 
the  expense  is  greater. 

The  joint  of  a  hub-and-spigot  pipe  is  made  sometimes  of 
clay,  but  in  this  country  cement  mortar  is  almost  universally 
used.  Clay  has  cheapness  alone  to  recommend  it  as  compared 
with  cement.  Other  materials  have  been  used  for  sewer-pipe 
joints,  such  as  the  Stanford  preparation,  a  tar-and-sulphur 
compound.  In  Germany  asphalt  has  recently  been  used  and 
good  results  reported.  Most  of  these  materials  are  more 
expensive  and  less  durable  than  Portland  cement,  and  are 


DETAIL   PLANS.  169 

probably  to  be  preferred  to  it  only  under  certain  circum- 
stances, if  at  all. 

A  glazed  clay  pipe  offers  a  poor  surface  for  cement  to 
adhere  to,  and  consequently  with  it  an  absolutely  tight  joint 
is  almost  impossible  of  construction.  After  a  short  period  of 
use,  however,  a  well-made  joint  of  good  cement  will  become 
so  stopped  with  matter  strained  from  out-filtering  sewage  as 
to  be  practically  water-tight.  But  if  the  head  of  ground- 
water  is  greater  than  that  of  sewage  the  flow  will  be  inward 
and  the  joint  will  probably  not  become  tighter  than  it  was  at 
construction.  Tighter  joints  could  probably  be  made  if  the 
glazing  were  omitted  or  removed  from  the  surfaces  in  contact 
with  the  cement. 

If  much  sewage  leaks  out  through  a  joint  there  is  danger 
that  the  remaining  fluid  will  not  be  sufficient  to  keep  the 
sewer  clean  of  deposits.  But,  as  just  stated,  such  a  condition 
seldom  continues  for  a  long  time  after  the  sewer  is  put  into 
use  if  the  joints  were  well  made. 

Several  modifications  of  the  ordinary  joint  have  been 
designed  to  overcome  this  difficulty,  such  as  roughening  the 
outside  of  the  spigot  end  and  the  inside  of  the  bell.  One 
style  of  patent  joint  is  shown  in  Plate  VIII,  Fig.  n.  Such 
complicated  joints  are  expensive  and  difficult  both  to  manu- 
facture and  to  lay,  and  are  seldom  used.  If  there  is  consider- 
able ground-water  it  is  better  to  lay  the  pipe  as  shown  in 
Plate  VII,  Fig.  3,  or  to  use  light-weight  or  second-quality 
cast  iron,  or  wrought  iron  or  steel.  Carefully  made  concrete 
or  brick  sewers  may  also  be  used  for  the  larger  sizes,  of  extra 
thickness  to  resist  percolation. 

The  amount  of  ground-water  which  may  leak  through  a 
cement  joint  depends  very  largely  upon  the  shape  of  the  bell 
and  the  manner  in  which  the  joint  is  made.  If  the  annular 
cement-space  in  the  bell  is  too  small  the  cement  is  likely  to 
be  improperly  compacted  therein  or  not  to  enter  at  all  at 


I/O  SEWERAGE. 

some  points.  Experiments  seem  to  show  that  the  deeper  the 
ring  of  cement  in  the  joint  the  less  the  leakage.  If  for  any 
reason  the  cement  draws  away  from  either  bell  or  spigot  a 
leak  is  caused.  Hence  it  seems  best,  particularly  in  wet 
soils,  to  use  extra  deep  and  wide  sockets.  The  present 
standard  of  width  is  f  inch  for  pipe  from  2  to  10  inches 
diameter  and  -^  inch  from  12  to  24  inches  diameter,  which, 
if  always  secured,  should  be  sufficient.  The  depth  of  joint  it 
would  be  well  to  have  at  least  ij  inches  greater  than  the 
thickness  of  the  pipe ;  2  inches  wo.uld  probably  be  better. 

With  poor  joints  the  amount  of  leakage  may  be  limited 
only  by  the  amount  of  ground-water,  but  with  the  best  of 
cement  joints  in  very  wet  ground  the  leakage  may  amount  to 
5000  to  20,000  gallons  per  day  per  mile  of  sewer.  In  very 
many  systems  it  is  more  than  ten  times  this  amount. 

Experiment  seems  to  show  that  neat  Portland  cement 
makes  the  tightest  joints,  Portland  cement  and  sand  I  :  I 
the  next,  natural  cement  and  sand  I  :  I  the  next,  and  natural 
cement  neat  the  most  porous  joint. 

Since  the  joint  is  the  weak  place  in  a  pipe,  the  fewer  joints 
there  are  the  better.  The  expense  of  laying,  also,  is  decreased 
by  decreasing  the  number  of  joints.  For  these  reasons  the  use 
of  3-foot  rather  than  2-foot  lengths  of  pipe  is  advised.  Vitri- 
fied clay  pipes  more  than  3  feet  long  have  not  as  yet  been 
manufactured  with  success,  but  3-foot  lengths  can  be  furnished 
by  most  pipe-manufacturers  at  the  same  price  per  foot  as  the 
2-foot  lengths.  Some  prefer  to  use  the  2-foot  lengths  when 
the  diameter  of  the  pipe  exceeds  15  or  1 8  inches,  as  the  3-foot 
lengths  of  the  larger  pipe  would  require  a  derrick  for  handling. 
Thirty-inch  pipe  is  generally  made  2j  feet  long. 

There  are  some  advocates  and  users  of  cement  sewer-pipe, 
the  most  important  in  this  country  being  the  city  (now 
borough)  of  Brooklyn,  N.  Y.,  which  has  used  it  almost 
exclusively  for  35  years  or  more.  It  has  the  advantage  over 


DETAIL   PLANS.  17 1 

clay  pipe  that  it  can  be  moulded  to  exactly  the  size  and  shape 
desired,  while  the  clay  shrinks  and  sometimes  warps  in  burn- 
ing. It  is  therefore  possible  to  obtain  a  sewer  with  a  more 
uniform  bore  by  using  cement  pipe;  also  to  obtain  the  advan- 
tage (not  very  considerable  under  most  circumstances)  of  a 
flat  base,  as  shown  in  Plate  VI,  Fig.  I. 

When  this  pipe  is  made  of  good  cement  and  sand  and  this 
is  properly  proportioned  and  mixed  it  should  give  a  material 
which  will  improve  with  age.  It  is,  however,  more  difficult 
to  detect  the  quality  of  a  cement  than  of  a  vitrified  clay  pipe, 
and  much  worthless  cement  pipe  has  consequently  been  put 
upon  the  market.  Clay  pipe  has  a  somewhat  smoother  sur- 
face, but  this  difference  grows  less  with  age,  owing  to  the 
coating  which  forms  on  each. 

Cement  pipe  weighs  from  50  to  100  per  cent  more  than 
clay  pipe  of  the  same  diameter,  and  hence  both  freight  and 
expense  of  handling  are  increased.  Good  cement  pipe  is  in 
most  places  more  expensive  than  good  clay  pipe. 

ART.  47.     MANHOLES,    LAMP-HOLES,    FLUSH-TANKS,  ETC, 

The  purpose  of  manholes,  as  the  name  implies,  is  to  give 
admittance  to  the  sewers,  which  is  necessary  for  the  purpose 
of  inspection  and  cleaning.  They  should  therefore  be  suffi- 
ciently large  to  permit  the  passage  through  them  of  a  man  of 
average  size. 

Manholes  are  in  general  built  immediately  above  a  sewer 
and  leading  from  it  to  the  ground-surface.  In  the  case  of 
some  large  sewers  in  Europe  they  are  built  at  one  side  of  the 
sewer  and  connected  with  it  by  an  underground  passage,  the 
chief  advantages  of  which  construction  are  the  greater  con- 
venience for  entering  and  the  avoiding  of  manhole-heads- in 
the  street-paving.  But  this  construction  is  very  expensive 
and  the  passage  is  liable  to  be  a  collector  of  filth. 


SEWERAGE. 

The  size  of  vertical  manholes  is  usually  24  inches,  although 
sometimes  only  22  or  even  20  inches,  diameter  at  the  top, 
increasing  towards  the  bottom  to  a  size  in  which  a  man  can 
work.  The  least  size  advisable  for  the  bottom  on  lines  of 
pipe  sewers  is  4  feet  circular  or  3  feet  by  4  feet  6  inches 
oval.  In  manholes  of  this  size  the  ordinary  operations  of 
inspection  and  cleaning  of  pipe  sewers  can  be  carried  on. 
There  is  no  particular  advantage  in  having  an  ordinary  man- 
hole of  more  than  5  feet  interior  diameter. 

Wherever  possible  the  sides  of  the  manhole  should  be  built 
vertical  from  the  side  benches  of  the  bottom  (ab  and  cd,  Plate 
VIII,  Fig.  5)  to  a  point  3  feet  above,  from  which  point  they 
may  be  brought  in  with  a  straight  batter  to  the  smaller  top, 
which  is  usually  circular.  Where  the  depth  of  the  top  of  the 
sewer  below  the  surface  is  less  than  7  feet  this  construction 
becomes  difficult,  owing  to  the  considerable  angle  which  the 
upper  walls  must  make  with  the  vertical.  The  slope  cannot 
well  begin  at  a  lower  point  than  that  stated  and  leave  work- 
ing-room at  the  bottom.  If  the  depth  of  sewer  is  more  than 
5  feet  this  difficulty  can  be  met  by  arching  the  walls  (see 
Plate  IX,  Fig.  2),  which  construction  requires  careful  work- 
manship. An  alternative  method,  especially  adapted  to  a 
depth  of  less  than  5  feet,  is  to  reduce  the  area  of  the  manhole 
near  the  top  by  an  offset,  using  either  a  brick  arch  or  an  iron 
beam  to  span  the  offset  (see  Plate  IX,  Fig.  3).  If  the  man- 
hole is  more  than  10  feet  deep  the  diameter  should  increase 
more  rapidly  for  the  first  3  feet  down  from  the  top,  being  at 
least  2  feet  9  inches  at  that  depth,  as  otherwise  descent 
through  the  shaft  will  be  difficult. 

Descent  through  the  manhole  can  be  made  by  means  of  a 
ladder  or  a  rope,  but  it  is  customary  to  build  steps  into  the 
wall  for  this  purpose.  These  may  consist  of  protruding 
bricks  or  stones  or  cast-  or  wrought-iron  pieces.  The  first 
offer  but  precarious  footing,  cast  iron  is  not  so  reliable  as 


DETAIL   PLANS. 


173 


Plate  .IX. 


FIG.  5.  CROSSING  MANHOLE. 


FIG.  7.  BROOKLYN,  (N.Y.) 

MANHOLE  COVER,  1896. 

AVE.  WEIGHT,HEAD,395  LB3. 

i(  ii        COVER,  130  " 


FIG.  10. 
PIPE  LAMPHOLE. 


FIG.  8. 
MANHOLE  BUCKET. 


FIG.  11. 
BRICK  LAMPHOLE. 


FIG.  9    VENTILATING 
MANHOLE  HEAD. 


174  SEWERAGE. 

wrought  and  costs  little,  if  any,  less;  the  last  is  therefore 
recommended.  These  steps  are  made  of  various  shapes. 
The  simplest  and  probably  as  good  as  any  is  one  made  of  a 
round  bar  bent  as  shown  in  Plate  IX,  Fig.  4.  The  steps 
should  be  placed  about  15  inches  apart  vertically,  and  either 
directly  under  each  other  or  alternating  on  each  side  of  a 
vertical  line,  the  former  in  narrow  shafts. 

Manholes  oval  at  the  bottom  are  well  adapted  to  locations 
where  there  are  no  intersecting  sewers;  those  circular,  to 
points  of  intersection. 

Where  one  sewer  crosses  another  without  intersecting  it 
a  manhole  of  special  construction,  permitting  of  inspecting 
each  sewer,  is  desirable.  Such  a  one  is  shown  in  Plate  IX, 
Fig.  5,  in  which  the  upper  sewer  is  continued  through  the 
manhole  by  an  iron  trough. 

While  at  the  junction  of  a  pipe  sewer-main  and  lateral  the 
latter  should  be  at  a  somewhat  higher  elevation  than  the 
former,  the  difference  in  elevation  of  the  crowns  of  the  two 
should  not  exceed  6  inches.  To  obtain  this  result  the  lateral 
may,  if  necessary,  be  lowered  2  or  3  feet  at  its  end  by  increas- 
ing the  grade  from  the  previous  manhole.  If  this  would 
increase  the  depth  of  excavation  by  more  than  3  or  4  feet  a 
drop  between  the  sewers  may  be  made  at  the  manhole.  This 
should  be  so  arranged  that  each  sewer  will  be  accessible  for 
cleaning.  The  drop  should  not  be  made  through  the  shaft  of 
the  manhole,  but  through  a  small  smooth  channel.  A  good 
design  is  that  shown  in  Plate  X,  Fig.  8. 

When  sub-drains  are  laid  under  large  sewers  arrangements 
for  cleaning  them  may  be  made  as  shown  in  Plate  VI,  Fig.  6, 
by  a  vertical  branch  opening  into  a  manhole,  or  if  they  are 
under  the  centre  of  the  sewer  such  a  pipe  may  open  into  the 
sewer-invert,  the  opening  being  ordinarily  tightly  closed  by  a 
cap  or  plug.  When  the  sub-drain  is  under  a  small  sewer  the 
branch  pipe  should  lead  into  a  manhole,  opening  either  in  the 


DETAIL   PLANS. 


175 


Plate  X. 


GRATING 

FIG.  2.  INLET. 


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//  ^V'Y 

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FIG.  5.  STONE  TOP  INLET 
WITH  CATCH-BASIN- 


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iji"    *nq 

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f  •""'• 
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—  -I. 

v-^  i 

T^ 

rnrr:  rtr 
r:i"!  ILJU 

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1  1 

FIG.  4. 

WROUGHT  fRON 
INJ-ET  GRATING, 


INSPECTION  HOLE 
GUARD,  a. 


FIG.  8.  DROP  MANHOLE. 


FiG.  9. 

MANflOLE  WITH  SU8DRAJN 
INSPECTION  HOLE. 


DEEP-CUT 
'HOUSE  CONNECTION*, 


SEWERAGE. 

sewer-invert  or,  better,  in  the  bench.  In  either  case  the 
opening  should  be  plugged  so  that  absolutely  no  sewage  can 
enter  it  (see  Plate  X,  Fig.  9). 

Manholes  of  special  design  will  be  required  by  unusual 
conditions,  but  in  all  the  three  principal  requirements  of  a 
manhole  should  be  met:  it  should  offer  easy  access  to  inspec- 
tion and  cleaning  of  the  sewer,  and  ventilation  of  the  same; 
it  should  also  be  so  proportioned  as  to  resist  the  pressure  of 
the  surrounding  earth.  For  this  last  purpose  the  curved  form 
is  better  than  the  polygonal. 

Manholes  for  sewers  larger  than  30  to  36  inches  are  usually 
built  up  from  the  sewer-arch  and  have  no  special  bottom  con- 
struction. The  sewer-invert  under  the  manhole  should  be 
reinforced,  however,  if  the  ground  is  at  all  yielding.  The 
manhole-shaft  is  sometimes  placed  on  one  side  of  the  sewer 
both  for  strength  and  for  facility  of  access  (see  Plate  IX, 
Fig.  6). 

The  foundation  of  a  manhole  should  be  perfectly  solid* 
If  the  soil  is  soft  a  plank  platform  may  be  used.  Owing  to 
the  irregular  shape  of  the  bottom  concrete  usually  gives 
better  results  as  to  strength,  shape,  and  imperviousness  than 
does  brick-work.  The  bore  of  each  sewer  should  be  continued 
through  the  bottom  by  a  smooth  channel  of  uniform  section 
and  slope,  either  straight  or  with  a  continuous  curve.  This 
channel  can  be  plastered  with  Portland  cement,  lined  with 
brick  or  with  split  vitrified  pipe.  The  last  method  gives  the 
smoothest  surface  and  is  the  one  most  likely  to  give  a  straight 
channel  of  uniform  size.  For  curved  channels,  if  split  bends 
of  the  desired  radius  cannot  be  had,  brick  plastered  with  Port- 
land cement  is  recommended.  The  channels  should  have 
vertical  sides  carried  up  to  a  point  at  least  f  as  high  above  the 
invert  as  the  top  of  the  sewer-pipe,  and  benches  should  slope 
up  to  the  sides  of  the  manhole  at  an  angle  of  at  least  10°  cr 
15°  with  the  horizontal. 


DETAIL   PLANS.  177 

The  manhole  walls  are  usually  built  of  brick,  8  inches  thick 
from  the  top  to  a  point  10  or  12  feet  below  the  surface,  and 
increasing  in  thickness  with  the  depth.  If  the  bottom  is  a 
circle  or  a  well-designed  oval  with  no  radius  greater  than  6 
feet  a  1 2-inch  wall  should  be  strong  enough  at  any  depth, 
unless  the  ground  is  a  quicksand  or  similar  material  or  is  very 
wet.  The  outside  of  the  manhole  should  be  plastered  with 
cement  mortar  to  keep  out  ground-water  or  water  used  in 
settling  the  trenches,  and  to  prevent  the  lifting  of  the  top 
foot  or  two  by  freezing  ground. 

The  top  of  the  manhole  is  generally  capped  with  an  iron 
casting  sufficiently  deep  to  permit  the  laying  close  to  it  of 
brick  or  stone  paving.  This  will  be  about  8  or  10  inches 
except  where  the  paving  is  made  for  heavy  or  city  traffic., 
where  it  may  need  to  be  12  or  18  inches. 

Whether  the  street  is  paved  or  not  each  manhole-heati-1 
should  be  surrounded  for  a  distance  of  at  least  2  feet  by  stone 
or  brick  paving  on  concrete  or  sand  foundation,  the  head 
being  set  \  to  £  inch  lower  than  the  paving. 

The  cover  should  be  sufficiently  strong  to  support  the 
heaviest  wheel-pressure.  It  should  be  provided  with  ventila- 
tion-holes giving  as  much  area  of  opening  as  possible.  Its 
upper  surface  should  be  roughened  to  provide  foothold  for 
horses.  The  ventilation-holes  should  be  through  the  elevated 
rather  than  through  the  depressed  parts  of  the  cover,  since  by 
this  construction  the  stoppage  of  the  holes  by  dirt  and  snow 
and  the  entrance  of  dirt  into  the  sewer  are  considerably 
lessened.  Such  a  manhole-head  and  -cover,  as  used  in 
Brooklyn,  N.  Y.,  is  shown  in  Plate  IX,  Fig.  7.  Covers  are 
sometimes  provided  with  locks  to  prevent  the  opening  of  the 
manhole  by  unauthorized  persons.  Much  trouble  is  in  some 
instances  caused  by  these  locks,  particularly  in  freezing 
weather.  A  better  plan  probably  is  to  make  the  covers  so 


SEWEXAGE. 

heavy  that  they  cannot  readily  be  raised  without  the  use  of 
some  strong  implement  adapted  to  this  purpose. 

More  or  less  dirt  will  be  sure  to  enter  through  the  ventila- 
tion-holes and  if  allowed  to  reach  the  bottom  of  the  manhole 
will  tend,  particularly  in  small  sewers,  to  form  stoppages.  To 
prevent  this  a  bucket  of  some  kind  should  be  suspended  under 
the  holes,  smaller  than  the  manhole-opening,  that  the  air  may 
pass  up  between  the  bucket  and  the  walls,  or  a  special  con- 
struction of  some  kind  should  be  designed  for  this  purpose 
(see  Plate  IX,  Figs.  8  and  9).  These  receptacles  should  be 
cleaned  before  they  become  filled  with  dirt,  for  which  purpose 
the  removable  bucket  of  Fig.  8  is  the  more  convenient. 
Another  objection  to  Fig.  9  is  the  larger  amount  of  street- 
surface  occupied  by  the  iron  head. 

Lamp-holes  may  be  from  8  to  12  inches  in  diameter  and 
are  placed  vertically  above  the  sewer.  They  are  sometimes 
made  by  placing  in  the  pipe-line  a  T  branch  pointing  upward 
and  resting  a  vertical  line  of  sewer-pipe  in  it.  This  is 
decidedly  poor  construction,  as  the  branch  pipe  is  liable  to  be 
crushed  by  the  weight.  The  upright  pipes  should  be  sup- 
ported by  a  foundation  of  brick  or  concrete  or  the  entire 
shaft  should  be  of  brick.  The  latter  is  much  to  be  preferred, 
since  the  pipe  construction  is  almost  sure  to  be  pushed  out  of 
line  by  the  settling  of  the  back-filling. 

The  foundation  of  a  lamp-hole  should  be  firm,  the  invert 
formed  as  shown  in  Plate  IX,  Fig.  n.  The  head  it  would 
be  well  to  provide  with  ventilation-holes,  but  this  is  seldom 
done. 

A  flush-tank  should  be  tight.  It  should  be  so  propor- 
tioned as  to  hold  the  required  amount  of  water  without 
increasing  the  head  on  the  sewer  beyond  the  limit  set  (Art. 
26).  The  flush-tank  is  usually  set  at  the  upper  end  of  a  sewer- 
line,  toward  which  much  sewer-air  rises,  and  the  sewer  should 
therefore  be  provided  at  that  point  with  ample  ventilation. 


DETAIL   PLANS.  179 

In  spite  of  this  many  flush-tanks  are  so  built  as  to  afford  the 
sewer  absolutely  no  ventilation,  forcing  the  adjacent  houses 
to  unwillingly,  and  usually  unknowingly,  provide  it.  Since 
flushing-siphons  cannot  permit  of  ventilation  through  their 
passages,  a  vent  should  be  furnished  the  sewer  just  below  the 
flush-tank.  It  is  advisable  to  combine  with  this  a  lamp-hole, 
as  in  Plate  X,  Fig.  I.  A  still  better  plan  is  to  place  a  venti- 
lating-manhole  just  below,  even  in  contact  with,  the  flush- 
tank. 

Flush-tanks  are  usually  built  of  brick  with  concrete 
bottoms,  the  whole  being  made  water-tight.  Concrete  or  iron 
would  probably  be  preferable  in  some  cases. 

The  automatic  flushing  appliances  in  common  use  act  on 
the  principle  of  the  siphon,  the  variations  being  in  the  method 
cf  starting  the  flow.  Some  have  no  moving  parts  whatever, 
such  as  the  Rhoads- Williams  and  Miller  tanks.  Of  those 
having  moving  parts  the  Van  Vranken,  which  has  a  balanced 
tipping-pan  at  the  foot  of  the  siphon,  is  probably  the  best 
known.  A  number  of  other  ideas  have  been  used  for  flush- 
tanks,  such  as  a  tank  on  trunnions,  which  tips  when  full  and 
returns  to  its  original  position  when  empty;  a  collapsing  tube 
which,  as  the  water  rises  in  the  tank,  is  extended  upward  by 
an  attached  float  until  it  reaches  its  full  length,  when  the 
water,  still  rising,  overflows  into  and  through  it  to  the  sewer, 
the  tube  meantime  collapsing. 

The  outlet  of  the  flush-tank  should  be  at  some  elevation, 
the  more  the  better,  above  the  sewer.  If  no  automatic  appli- 
ance is  used  the  opening  of  the  flush-tank  may  be  in  the 
bottom,  stopped  by  a  plug  or  cap,  which  is  raised  by  an 
attached  chain  when  the  tank  is  full;  or  it  may  be  in  the  side 
and  be  opened  and  closed  by  a  valve,  either  sliding  or  hinged. 

If  water  is  led  to  the  flush-tank  by  a  pipe  this  should  be 
kept  below  the  effect  of  frost,  turning  and  rising  to  a  higher 
level  inside  the  flush-tank  if  necessary. 


1 8O  SE IV ERA  GE. 

Inlets  are  made  with  and  without  catch-basins  (see  Art. 
41),  and  the  openings  are  sometimes  vertical,  sometimes  hori- 
zontal, and  sometimes  inclined.  Their  purpose  being  to- 
admit  water  from  the  roadway  to  the  sewer,  the  opening  of 
each  inlet  should  be  sufficiently  large  to  admit  all  the  water 
which  can  reach  it  from  the  heaviest  rain  whose  run-off  the 
sewer  is  designed  to  carry.  It  may  be  so  designed  that  a 
smaller  one  leading  to  a  house-sewer  shall  pass  the  water  from 
small  rains  or  the  first  washings  of  a  rain,  while  another  larger 
one  leads  to  a  storm-sewer.  The  opening  should  be  at  the 
gutter  where  the  water  flows,  and  which  may  be  slightly 
depressed  at  this  point.  If  horizontal  in  the  bottom  of  the 
gutter  one  large  opening  is  not  permissible,  but  smaller  ones, 
into  which  neither  carriage-wheels  nor  feet  of  horses  or 
pedestrians  can  enter,  must  be  used.  The  plate  through 
which  these  holes  are  made  must  be  able  to  support  the  most 
heavily  loaded  wheels  which  are  likely  to  come  upon  it.  But 
this  need  not  include  exceptionally  heavy  loads,  which  usually 
keep  to  the  centre  of  the  street. 

If  the  openings  are  through  the  face  of  the  curb,  in  a  plane 
either  vertical  or  slightly  inclined,  they  may  be  much  larger. 
In  some  cases  one  large  opening  is  used,  entirely  unprotected, 
through  which  children  could  and  sometimes  do  fall.  Except 
for  this  danger  such  a  clear  waterway  is  an  excellent  arrange- 
ment. But  it  is  advisable  to  so  place  one  or  more  bars  across 
the  opening  as  to  remove  the  danger  referred  to. 

The  total  area  of  opening  required  may  be  found  approxi- 
mately by  the  hydraulic  formulas  for  flow  through  horizontal 
or  vertical  orifices  or  over  weirs,  as  the  case  may  be.  In  the 
case  of  openings  less  than  2  inches  across  in  any  direction  an 
additional  allowance  should  be  made  for  the  occasional 
stoppage  of  some  of  them  by  leaves,  paper,  etc.  The  vertical 
openings,  being  larger,  are  less  liable  to  stoppage.  If  hori- 


DETAIL   PLANS.  l8l 

zontal  openings  in  the  gutter  are  in  the  shape  of  slots  they 
should  run  across  the  line  of  the  gutter. 

Between  the  openings  and  the  sewer  the  channel  should 
be  straight  or  have  as  easy  bends  as  possible,  that  the  run-off 
may  have  an  uninterrupted  flow.  The  use  of  a  catch-basin 
greatly  interferes  with  this,  the  water  seething  and  whirling 
in  it  during  storms;  consequently  the  channel  connecting  it 
with  the  sewer  should  be  larger  than  if  a  simple  inlet  were 
used.  In  some  instances  a  pipe  leads  directly  from  the  open- 
ing to  the  sewer,  either  with  or  without  a  water-seal  trap.  It 
is  better,  however,  to  obtain  a  more  substantial  structure  by 
setting  under  the  opening  a  small  basin  with  a  curved  bottom 
from  which  the  pipe  leads  directly  to  the  sewer.  Where  the 
opening  is  horizontal  the  basin  is  desirable  to  support  the 
weight  which  may  come  upon  the  grating  and,  where  a  trap 
is  used,  to  enable  it  to  be  placed  below  danger  of  freezing. 
It  also  facilitates  inspection  and  cleaning  of  the  connection- 
pipe  (see  Plate  X,  Fig.  2).  Figs.  3  and  4  show  two  designs 
for  inlet-gratings,  the  latter  particularly  adapted  to  admitting 
large  quantities  of  water. 

A  catch-basin  usually  consists  of  a  well  under  the  inlet- 
opening  and  below  the  connection-pipe  to  catch  the  heavier 
matters.  It  is  sometimes  placed  between  the  inlet  and  the 
sewer  on  the  line  of  the  connection-pipe,  and  sometimes  at 
the  sewer  in  connection  with  a  manhole.  To  be  at  all 
efficient  it  should  extend  more  than  18  inches  below  the  con- 
nection-pipe, since  a  heavy  rain  will  keep  the  water  in  it  so 
stirred  up  as  to  wash  out  any  deposits  above  that  point. 
The  bottom  of  the  catch-basin  should  be  covered  with  a  flag- 
stone or  the  most  substantial  of  concrete-  or  brick-work. 

Inlet  and  catch-basin  wells  may  be  built  of  concrete  or  of 
stone,  but  are  usually  of  brick.  Catch-basin  wells  should  be 
water-tight,  that  water  may  constantly  cover  the  contents  and 
lessen  their  odors.  The  gratings  of  catch-basins  should  be 


1 82  SEWERAGE. 

removable  or  the  basins  should  be  provided  with  manhole- 
openings  and  the  wells  be  sufficiently  large  to  be  entered  for 
the  inspection  and  cleaning  of  the  connection-pipes. 

When  the  inlet-opening  is  vertical  the  well  is  usually 
under  the  curbing  or  sidewalk,  and  access  to  it  is  through  a 
manhole-opening  in  the  sidewalk.  There  is  a  great  variety  of 
inlet-tops  for  such  construction,  both  cast  iron  and  stone 
being  used.  The  latter,  where  not  too  expensive,  is  usually 
preferable,  being  neater,  more  durable,  and  usually  more  like 
the  contiguous  sidewalk  material  than  cast  iron.  A  stone- 
topped  inlet  is  shown  in  Plate  X,  Fig.  5,  an  iron-topped  one 
in  Fig.  6. 

Traps  are  frequently  placed  in  catch-basins  or  the  con- 
necting-pipes to  prevent  the  exit  of  sewer-air,  unwisely  the 
author  thinks  (see  Art.  41).  The  outside  trap  is  usually  a 
running  or  P  pipe  trap.  Many  varieties  of  inside  trap  have 
been  designed,  both  fixed  and  movable.  The  former  should 
not  prevent  access  to  the  connection-pipe  and  hence  should 
be  at  least  15  inches  from  its  opening.  Traps  with  movable 
parts  should  be  as  simple  as  possible  in  construction  and 
compel  the  outflowing  water  to  make  the  least  possible 
number  of  angular  changes  of  direction. 

Instead  of  placing  a  catch-basin  at  each  inlet  it  is  some- 
times preferable  to  place  silt-basins  along  the  line  of  the  sewer 
at  intervals  of  1000  feet  or  more,  with  a  manhole  over  each 
for  ventilation  and  cleaning.  These  are  particularly  applica- 
ble to  flat  grades  of  storm  sewers  in  the  separate  system. 
They  consist  of  an  enlargement  of  the  sewer,  and  a  depression 
of  a  foot  or  more  in  its  invert,  into  which  the  heavier  silt  is 
washed,  and  from  which  it  can  be  removed  more  easily  than 
when  deposited  along  a  stretch  of  sewer.  These,  however, 
should  not  be  used  to  encourage  deposit,  but  only  when 
deposits  would  occur  along  the  sewer  if  they  were  not  pro- 
vided. Their  advantage  over  inlet  catch-basins  is  that  the 


DETAIL   PLANS.  183 

odors  reach  the  outer  air  further  from  pedestrians,  and  that 
the  difficulty  and  cost  of  cleaning  is  not  so  great.  They 
should  be  used  in  sewers  which  carry  house-sewage  in  excep- 
tional cases  only.  Inlet  catch-basins  are  generally  preferable 
on  lines  of  combined  sewers  where  much  heavy  dirt  reaches 
the  inlet,  or  on  storm-sewers  where  such  dirt  is  washed  in  in 
very  large  quantities. 

ART.  48.     INTERCEPTORS  AND  OVERFLOWS. 

The  best  form  of  interceptor  to  be  employed  is  determined 
largely  by  the  character  of  the  system  at  the  point  of  inter- 
ception. If  the  house-sewage  is  to  be  intercepted  from  tribu- 
tary sewers  which  originally  discharged  into  a  near  body  of 
water,  the  interceptor  shown  in  Plate  XI,  Fig.  I,  may  be 
used.  This  "  leaping  weir,"  it  is  believed,  was  first  used  by 
Baldwin  Latham  about  1876.  The  exact  length  of  opening 
required  in  the  invert  can  be  only  approximately  determined. 
It  may  be  made  smaller  than  is  thought  necessary  and  cut  to 
the  right  size,  which  is  ascertained  by  trial,  after  the  sewer  is 
in  use.  It  will  also  probably  be  desirable  to  increase  the 
length  from  time  to  time  as  the  amount  of  house-sewage 
increases.  The  principal  objection  to  this  form  of  interceptor 
is  that,  although  the  storm-water  may  leap  the  opening,  much 
of  the  sand  and  other  heavy  matter  carried  along  the  invert 
of  the  combined  sewer  will  fall  into  the  small  intercepting 
sewer  and  be  deposited  there. 

An  interceptor  which  meets  this  objection,  but  which  may 
more  properly  be  called  a  divertor,  is  shown  in  Plate  XI, 
Fig.  2.*  The  flap-valve  shown  is  closed  by  the  rising  of  the 
float,  which  occurs  when  the  amount  of  sewage  becomes 
greater  than  it  is  desired  that  the  house-sewer  carry.  The 
joints  of  the  mechanism  should  be  of  bronze.  A  sewer  does 
not  offer  the  best  conditions  for  the  continued  proper  working 

*  See  Engineering  Record,  vol.  xxxil,  p.  41. 


1 84 


SEWERAGE. 


£late  XI. 


FIG.  1 .  INTERCEPTOR  (LEAPING  WETRX 


FIG.  2.  INTERCEPTOR  (DIVERTING) 


FIG.  10. 

FIG.  9.  DEEP-CUT  HOUSE  HOUSE  CONNECTKDN 

FIG.  7."  FIG.  8.  CONNECTION  IN  R.OCK.  INSPECTION  HOLE. 

SUB-DRAJH,  SUB-DRAINV 


DETAIL   PLANS.  1 8$ 

of  any  mechanism  therein,  but  one  so  simple  as  this  should 
give  little  trouble  in  its  maintenance. 

When  a  sewer,  because  of  improper  designing  or  of 
changed  conditions,  becomes  too  small  to  carry  all  the  sewage 
coming  to  it,  the  excess  above  its  capacity  may  be  diverted 
to  and  carried  by  a  relief-sewer  or  -sewers.  A  relief-sewer 
may  cross  under  and  receive  the  excess  from  several  gorged 
sewers,  or  a  single  sewer  may  overflow  into  several  relief- 
sewers  placed  at  intervals  along  its  length  and  leading  to 
near-by  outlets. 

An  outlet  sewer-main  to  combined  sewers  is  sometimes 
provided  with  overflow  outlets  at  several  points  to  avoid 
increasing  the  size  of  the  main  beyond  the  smallest  necessary 
dimension,  which  is  usually  that  which  will  carry  sufficient 
storm-water  to  afford  such  dilution  to  the  house-sewage  as 
will  render  it  unobjectionable  to  discharge  this  into  an 
adjacent  stream.  The  diversion  into  such  a  relief-sewer  or 
relief  outlet  is  ordinarily  made  by  means  of  an  overflow,  con- 
structed as  shown  in  Plate  XI,  Fig.  3,  or  as  in  Fig.  4,  where 
the  relief-sewer  was  constructed  after  the  smaller  sewers  had 
long  been  in  use. 

ART.  49.    INVERTED  SIPHONS;  SUB-DRAINS;  FOUNDATIONS. 

Inverted  siphons  are  usually  circular  in  section,  since 
always  flowing  full;  usually  of  metal,  since  always  under 
pressure,  although  the  metal  may  be  lined  with  brick  or  other 
material.  The  size  required  has  already  been  referred  to. 
When  laid  under  water  they  should.be  so  weighted  or  covered 
with  earth  or  stone  as  to  prevent  their  floating  when  pumped 
empty  for  inspection  or  cleaning,  and  should  be  absolutely 
tight.  The  inverted  siphon  is  made  sometimes  to  slope  from 
both  ends  to  a  point  near  mid-length,  sometimes  with  a 
vertical  drop  at  one  end,  sometimes  at  both  ends.  The  first 


1 86  SEWERAGE. 

should  be  adopted  only  when  the  siphon  is  sufficiently  large 
to  permit  the  entrance  of  a  man.  When  not  of  such  a  size  it 
should  be  straight  from  end  to  end.  This  will  usually  require 
a  shaft  at  one,  sometimes  at  each,  end,  which  may  also  serve 
as  a  manhole.  It  is  in  most  cases  advisable  to  place  a  catch- 
basin  at  the  foot  of  such  a  shaft,  although  in  place  of  this  a 
basin  in  the  bottom  of  an  enlargement  of  the  sewer  just  above 
the  siphon  is  sometimes  employed.  A  siphon  with  catch- 
basins  is  shown  in  Plate  XI,  Fig.  5,  the  valves  on  the  ends  of 
each  siphon-pipe  permitting  either  siphon  to  be  closed  to 
sewage  and  pumped  out  for  inspection,  while  the  other  is  in 
use. 

Unless  a  siphon  under  water  is  of  large  size  and  in  tunnel 
or  laid  in  a  trench  in  a  rocky  bottom  it  should  be  protected 
from  undermining  by  currents,  or  movement  by  shifting 
bottoms  or  channels.  This  protection  is  usually  afforded  by 
driving  a  row  of  sheet-piling  on  each  side  of  the  pipe,  the 
space  between  these  being  in  most  cases  excavated  and  filled 
with  concrete.  The  softer  the  material  in  the  bottom  and  the 
stronger  the  currents  the  deeper  the  sheeting  should  be 
driven.  If  the  bottom  is  too  hard  to  permit  of  driving  sheet- 
ing, large  stone  rip-rap  may  be  placed  on  both  sides  and  over 
the  siphon. 

A  sewer  must  sometimes  pass  either  under  or  over  art 
obstruction — such  as  a  water-main,  another  sewer,  etc. — by  a 
siphon,  either  inverted  or  erect.  The  latter  requires  greater 
care  in  construction  and  constant  attention  to  maintain  a 
vacuum  at  the  summit,  and  the  former  is  in  the  majority  of 
cases  the  preferable  construction.  Such  a  siphon  is  usually  a 
few  feet  in  length  only  and  under  but  little  head.  A  man- 
hole  should  be  placed  over  or  near  it  when  the  sewer  is  24 
inches  or  more  in  diameter,  since  it  will  probably  need  more 
frequent  cleaning  than  the  other  parts  of  the  line.  If  the 
sewer  is  less  than  24  inches  diameter  a  manhole  should  be 


DETAIL   PLANS.  187 


placed  at  the  upper  end  of  the  siphon  (which  should  be 
straight  from  end  to  end),  and  at  the  lower  end  also,  although 
a  lamp-hole  may  be  substituted  here  if  the  siphon  is  not  over 
150  feet  long,  and  makes  only  an  angle  and  not  a  vertical  rise 
at  this  point.  For  such  a  case  see  Plate  XI,  Fig.  6. 

Sub-drains  are  placed  either  directly  beneath  the  sewer  or 
at  one  side  of  the  trench.  When  there  are  no  artificial  foun- 
dations under  the  sewer  the  latter  position  is  to  be  preferred, 
but  is  in  some  instances  much  more  difficult  and  expensive, 
particularly  in  quicksand.  The  sub-drain  should  be  sur- 
rounded with  broken  stone  or  clean  gravel,  varying  preferably 
from  the  size  of  a  hickory-nut  to  that  of  a  pea.  There  should 
be  at  least  3  inches  of  this  under  the  drain  and  6  inches  at  its 
sides  and  top.  In  quicksand  or  similar  material  these  dimen- 
sions should  be  increased  50  to  100  per  cent.  This  stone 
should  be  well  compacted  to  prevent  future  settlement.  The 
joints  of  the  drain  should  be  slightly  open  and  a  5-  or  6-inch 
strip  of  cheese-cloth  or  burlap  wrapped  around  the  pipe  at  the 
joint  to  keep  out  the  dirt.  Or,  if  bell-and-spigot  pipe  is 
used,  a  piece  of  jute  may  be  calked  loosely  into  the  joint  for 
this  purpose. 

If  a  sewer  were  laid  directly  over  this  there  would  be 
danger  of  a  settlement  of  the  same  and  of  leakage  resulting. 
For  this  reason  the  sub-drain  should  be  laid  at  one  side  of  the 
trench  when  the  soil  is  firm,  as  in  Plate  XI,  Fig.  7.  In  quick 
or  running  sand  this  is  practically  impossible  unless  the  trench 
is  very  wide  or  unless  close  sheathing  be  driven  on  each  side 
of  the  sub-trench  and  carried  below  its  bottom;  such  sheath- 
ing not  to  be  removed  after  the  sub-drain  is  laid.  It  would 
usually  be  better  and  cheaper  than  this  to  lay  the  sub-drain 
in  the  centre  of  the  trench  (which  must  of  course  be  close- 
sheathed  in  quicksand),  and  on  the  stone  filling,  when  levelled 
off,  to  place  a  continuous  platform  on  which  to  lay  the  sewer. 
Such  construction  is  shown  in  Plate  XI,  Fig.  8.  A  still 


1 88  SEWERAGE. 

better  construction  in  any  but  firm  soils  is  to  lay  a  pipe  sewer 
in  concrete,  as  in  Plate  VII,  Fig.  3.  Where  a  foundation  is 
necessary  for  the  sewer  the  sub-drain  construction  is  easily 
arranged.  See  Plate  VI,  Fig.  6,  and  Plate  VII,  Fig.  10. 

The  sub-drain  should  be  laid  to  grade  as  carefully  as  the 
sewer  itself.  It  is  seldom  that  a  sub-drain  can  be  so  arranged 
that  inspection  can  be  made  of  it,  and  therefore  perfectly 
straight  alignment  is  not  necessary;  but  there  should  be  no 
sharp  angles  in  its  line,  which  might  cause  obstructions  or 
interfere  with  the  future  cleaning  of  it.  If  cellars  and  base- 
ments are  to  be  connected  with  this  drain  Y  branches  should 
be  inserted  to  permit  of  such  connections,  and  should  be 
covered  similarly  to  the  house-sewer  branches. 

When  house  or  combined  sewers  are  placed  with  their  tops 
more  than  4  or  5  feet  lower  than  the  average  cellar  depth  in 
that  locality  it  is  advisable  to  place  a  standing  house-connec- 
tion above  each  branch,  bringing  it  to  within  3  to  5  feet  of 
the  average  depth  of  the  cellar  bottoms,  but  stopping  at  least 
7  or  8  feet  from  the  surface.  This  is  to  avoid  compelling 
each  householder  along  the  line  to  dig  down  to  a  deep  sewer 
branch  in  order  to  make  a  connection.  These  standing  con- 
nections are  built  while  the  sewer-trench  is  open,  and  are 
covered  at  the  top  with  a  cap  or  cover  similar  to  house- 
branches.  They  should  not  merely  rest  in  the  branch,  but  a 
foundation  of  concrete  or  brick  masonry  should  support  each. 
The  vertical  pipes  should  be  held  in  place  during  back-filling, 
as  by  stakes  driven  into  the  bank.  In  the  case  of  a  rock  cut, 
or  where  the  banks  are  not  firm,  the  standing  connection  may 
be  inclosed  by  a  vertical  trough  of  planks,  between  which  and 
the  pipe  earth  is  packed,  this  trough  being  held  firmly  in 
place  until  the  trench  is  filled  and  tamped.  If  the  banks  are 
liable  to  cave,  sheathing  should  be  driven  at  each  such  con- 
nection, and  neither  it  nor  the  braces  removed  when  the 
trench  is  filled.  A  standing  house-connection  in  firm  soil  is 


DETAIL   PLANS.  189 

shown  in  Plate  X,  Fig.  7.  One  in  a  rock  cut  is  shown  in 
Plate  XI,  Fig.  9. 

A  sewer  in  soft  soil,  like  any  other  structure,  requires  a 
foundation.  Since  the  weight  is  not  comparatively  great  the 
service  of  the  foundation  is  more  often  to  distribute  the  pres- 
sure and  prevent  local  settling  or  heaving  than  to  prevent  the 
subsidence  of  the  sewer  as  a  whole.  This  purpose  is  usually 
achieved  by  use  of  a  cradle  (Plate  VI,  Fig.  4)  or  a  platform 
of  plank  (Plate  VI,  Fig.  5),  the  former  in  comparatively  firm 
soils  like  damp  sand  or  loam,  the  latter  in  swamp-muck, 
quicksand,  etc.  Where  muck  or  other  soft,  water-sogged  soil 
is  encountered  it  may  be  necessary  to  drive  piles  and  rest  a 
timber  platform  upon  these,  Such  a  foundation  is  shown  in 
Plate  VI,  Figs.  3  and  6.  Where  a  platform  is  used  it  is 
necessary  to  fill  the  sub-invert  spaces  of  the  sewer  with 
masonry.  All  sewers  in  soft  soils  should  have  their  inverts 
arching  downward  to  resist  the  upward  thrust  of  the  ground 
between  the  side  walls,  since  the  weight  of  the  masonry  is 
largely  concentrated  in  these  walls. 

In  rock  excavations  no  part  of  the  pipe  sewer  should  come 
within  6  inches  of  the  rock  bottom,  and  the  space  between 
this  and  the  sewer  should  be  filled  with  sand  or  gravel 
thoroughly  tamped  to  prevent  settlements  of  the  invert;  or  the 
pipes  should  be  bedded  in  concrete,  in  which  case  the  rock 
may  be  taken  out  only  to  the  under  side  of  the  pipe.  If  the 
sewers  are  built  of  masonry  this  should  be  carried  to  rock 
everywhere  under  the  invert. 


CHAPTER    IX. 
SPECIFICATIONS,   CONTRACT,    ESTIMATE   OF  COST. 

ART.  50.     DEFINITION  AND  CLASSIFICATION  OF  SPECIFICA- 
TIONS. 

PUBLIC  work  is  frequently,  if  not  in  the  majority  of  cases, 
done  by  contract  by  a  "  party  of  the  second  part  "  who  is 
paid  for  this  work  by  the  city,  the  "  party  of  the  first  part." 
That  the  contractor  shall  do  the  work  as  the  city  desires  it  is 
necessary  that  he  be  instructed  what  is  desired  and  that  he 
bind  himself  to  follow  the  instructions.  This  should  all  be 
recorded  in  writing  for  the  protection  of  both  the  city  and  the 
contractor.  The  agreement  to  perform  the  work  on  the  one 
hand  and  to  pay  for  the  same  on  the  other  is  called  a  contract 
and  is  generally  accompanied  by  a  bond  under  which  the  con- 
tractor places  himself  to  perform  the  work  as  directed. 

The  directions,  called  "  specifications, "  "consist  of  a 
series  of  specific  provisions,  each  one  of  which  defines  and 
fixes  some  one  element  of  the  contract.  These  clauses  relate, 
in  general:  first,  to  the  work  to  be  done;  second,  to  the 
business  relations  of  the  two  parties  to  the  contract." 
(Johnson's  "  Engineering  Contracts  and  Specifications/') 
The  clauses  in  specifications  for  sewer  construction  referring 
to  the  work  to  be  done  may  be  classified  as  those:  first, 
defining  the  character  of  the  material  to  be  employed ; 
second,  giving  directions,  dimensions,  etc.,  for  excavating 

190 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.      IQI 

and  back-filling;  third,  setting  forth  the  methods  to  be 
employed  in  the  construction  of  the  sewer-barrel  and  appur- 
tenances, including  foundations;  fourth,  stating  the  require- 
ments of  the  completed  work,  tests  to  be  made,  etc. ;  fifth, 
giving  general  directions  for  the  conduct  and  maintenance  of 
the  work,  employment  of  labor,  etc.  Disposal  plants  will 
require  separate  specifications,  varying  with  the  character  of 
the  disposal  employed.  No  general  form  for  sucji  can  be 
given.  Other  special  features  of  a  system  will  call  for  special 
clauses. 

The  clauses  relating  to  the  business  relations  of  the  two 
parties  to  the  contract  may  be  classified  as  relating  to:  first, 
time  of  commencement  and  of  completion  and  rate  of  prog- 
ress of  the  work;  second,  character  of  labor  and  appliances 
to  be  employed  ;  third,  measurement  of  and  payments  for  the 
work;  fourth,  contractor's  protection  of  and  responsibility 
for  lives  and  property;  fifth,  abandonment,  cancellation, 
assignment  of  contract,  etc.;  sixth,  definition  of  names  and 
terms  employed. 

The  specifications  are  generally  accompanied  by  a  set  of 
plans  which  form  a  part  of  the  specifications  and  contract. 
These  together  should  set  forth  the  work  to  be  done  so  clearly 
as  to  leave  no  point  for  future  dispute.  Care  should  be  taken 
that  contradictory  instructions  are  not  given,  but  that  all 
parts  of  both  plans  and  specifications  mutually  agree.  Too 
great  profuseness  should  be  avoided  as  confusing  to  con- 
tractor, inspector,  and  engineer.  Many  engineers  insert  pro- 
visions which  they  have  no  intention  of  enforcing  under 
ordinary  conditions,  merely  to  be  on  the  safe  side,  or  which 
aim  at  theoretic  perfection  of  details  which  cannot  be  attained 
in  practice  (of  which  fact  their  inexperience  may  make  them 
ignorant).  The  fact  that  some  clauses  in  a  specification 
cannot  be  enforced  is  apt  to  detract  from  the  effectiveness  of 
the  others.  It  is  better  to  make  only  such  requirements  as 


IQ2  SEWERAGE. 

experience  shows  are  desirable  and  practicable  and  give  the 
contractor  to  understand  that  these  will  be  rigidly  enforced. 

No  foresight  can  predict  all  the  emergencies  which  may 
arise  in  sewer  construction.  To  provide  for  these  it  must  be 
agreed  that  the  engineer  can  modify  plans  or  methods  of  work 
during  construction,  as  well  as  increase  or  decrease  quanti- 
ties. Work  not  at  first  specifically  provided  for  may  be  made 
the  subject  of  separate  contract,  or  if  but  small  in  quantity 
may  be  done  under  the  original  contract  as  extra  work,  to  be 
paid  for  at  its  cost  plus  such  a  percentage  for  profit  (generally 
10  or  15  per  cent)  as  is  fixed  in  the  contract. 

ART.  51.     SPECIFICATIONS  FOR  MATERIALS. 

A  set  of  specifications  for  sewer  construction  will  be  given 
and  discussed  in  the  succeeding  pages.  Some  alterations  and 
additions  will  probably  be  required  to  adapt  them  to  any  par- 
ticular case,  but  it  is  thought  that  they  will  be  of  considerable 
service  as  an  illustration  of  both  matter  and  form.  Clauses 
in  brackets  are  given  as  alternatives,  the  one  preferred  by  the 
author  being  placed  first;  the  same  also  holding  true  with 
reference  to  the  lettered  paragraphs. 

Paragraph  I.  a.  Sewer-pipe. — All  pipe  and  specials, 
unless  otherwise  specified,  shall  be  of  the  best  quality, 
salt-glazed,  vitrified  clay  sewer-pipe  of  the  hub-and-spigot 
pattern;  both  body  and  bell  shall  [have  a  thickness  not  less 
than  y1^  the  inside  diameter  of  the  pipe]  [be  of  standard 
thickness].  Each  hub  shall  be  of  sufficient  diameter  to 
receive,  to  its  full  depth,  the  spigot  end  of  the  next  following 
pipe  or  special  without  any  chipping  whatever  of  either,  and 
also  leave  a  space  of  not  less  than  one  half  inch  all  around  for 
the  cement-mortar  joint;  it  shall  also  have  a  depth  from  its 
face  to  the  shoulder  of  the  pipe  on  which  it  is  moulded  at 
least  2  inches  greater  than  the  thickness  of  said  pipe.  Straight 


SPECIFICATIONS,   CONTRACT,  ESTIMATE    OF  COST.      1 93 

and  curved  pipe  having  diameters  up  to  and  including  15 
inches  shall  be  furnished  in  3-foot  lengths.  Branches  may  be 
in  2-foot  lengths.  All  pipe  and  specials  shall  be  sound  and 
well  burned,  with  a  clear  ring,  well  glazed  and  smooth  on  the 
inside  and  free  from  broken  blisters,  lumps,  or  flakes  which  are 
thicker  than  \  the  nominal  thickness  of  the  pipe  and  whose 
largest  diameters  are  greater  than  -J  the  inner  diameter  of  said 
pipe;  and  pipe  and  specials  having  broken  blisters,  lumps,  and 
flakes  of  any  size  shall  be  rejected  unless  the  pipe  can  be  so 
laid  as  to  bring  all  of  these  defects  in  the  top  half  of  the 
sewer.  No  pipe  having  unbroken  blisters  more  than  J-  inch 
high  shall  be  used  unless  these  blisters  can  be  placed  in  the 
top  of  the  sewer.  Pipes  or  specials  having  fire-checks  or 
cracks  of  any  kind  extending  through  the  thickness  shall  be 
rejected. 

No  pipe  shall  be  used  which,  designed  to  be  straight, 
varies  from  a  straight  line  more  than  -J  inch  per  foot  of  length; 
nor  shall  there  be  a  variation  between  any  two  diameters  of  a 
pipe  greater  than  -£-%  the  nominal  diameter. 

No  pipe  shall  be  used  which  has  a  piece  broken  from  the 
spigot  end  deeper  than  i£  inches  or  longer  at  any  point  than 
£  the  diameter  of  the  pipe;  nor  which  has  a  piece  broken  from 
the  bell  end  if  the  fracture  extends  into  the  body  of  the  pipe, 
or  if  its  greatest  length  is  greater  than  f  the  diameter  of  the 
pipe,  or  if  such  fracture  cannot  be  placed  at  the  top  of  the 
sewer.  Any  pipe  or  special  which  betrays  in  an/  manner  a 
want  of  thorough  vitrification  or  fusion  or  the  use  of  improper 
or  insufficient  materials  or  methods  in  its  manufacture  shall 
be  rejected. 

(Many  engineers  specify  a  depth  of  bell  only  I  inch  ' '  greater 
than  the  thickness  of  said  pipe,"  but  it  is  difficult  to  make 
tight  joints  in  actual  practice  with  such  bells.  Frequently  the 
defects  of  sewer-pipe  are  not  referred  to  in  detail,  but  the 


194  SEWERAGE. 

acceptance  or  rejection  made  optional  with  the  engineer  or 
inspector.  • 

If  cement  pipe  is  used  the  following  paragraph  may  be  sub- 
stituted for  i.  a.) 

Paragraph  i.  b.  Sewer-pipe. — All  pipe  and  specials, 
unless  otherwise  specified,  shall  be  of  the  best  quality  of 
cement  sewer-pipe,  of  the  [hub-and-spigot]  [bevelled-joint] 
pattern;  it  shall  have  a  thickness  not  less  than  -|  inch  plus 
Y1^  the  diameter  of  the  pipe.  [Each  hub  shall  be  of  sufficient 
diameter  to  receive,  to  its  full  depth,  the  spigot  end  of  the 
next  following  pipe  or  special,  without  any  chipping  whatever 
of  either,  and  also  leave  a  space  of  not  less  than  £  inch  all 
around  for  the  cement-mortar  joint;  it  shall  also  have  a  depth 
from  its  face  to  the  shoulder  of  the  pipe  on  which  it  is 
moulded  at  least  I  inch  greater  than  the  thickness  of  said 
pipe.]  [The  bevel  on  each  pipe  shall  be  at  least  25  per  cent 
longer  than  the  thickness  of  said  pipe,  with  an  even  and  firm 
edge.] 

All  pipe  shall  be  in  3-foot  lengths  and  in  section  shall 
truly  correspond  to  their  nominal  shapes.  Each  pipe  shall 
have  a  flat  base  making  exact  right  angles  with  the  vertical 
axis  of  the  pipe  and  with  a  width  equal  to  f  the  interior 
horizontal  diameter  of  said  pipe.  The  inside  surface  of  the 
pipe  shall  be  smooth  and  true,  and  no  pipe  shall  be  patched 
with  cement  or  otherwise.  Any  pipe  will  be  rejected  which 
is  not  of  fine,  sound,  and  dense  material  throughout,  or  which 
shows  the  use  of  poor  materials  or  imperfect  mixing  or  com- 
pacting. 

Paragraph  2.  a.  Drain-pipe. — Pipe  for  sub-drains  shall  be 
of  vitrified  clay  sewer-pipe  in  I-  or  2-foot  lengths  [of  the  hub- 
and-spigot  pattern]  [without  bells  or  sleeves].  It  shall  com- 
ply with  the  specifications  for  sewer-pipe  in  so  far  as  these 
refer  to  thickness,  quality,  and  vitrification  of  material, 
blisters,  lumps,  flakes,  cracks,  and  breaks;  except  that  the 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.      1 95 

engineer  may  at  his  option  accept  pipe  having  small  fire- 
cracks  or  checks. 

Paragraph  2.  b.  Drain-pipe. — Pipe  for  sub-drains  shall  be 
composed  of  the  best  quality  of  drain-tile  of  [circular]  [horse- 
shoe] cross-section  in  [one-]  [two-]  foot  lengths.  They  shall 
be  hard-burned  and  without  cracks  or  any  considerable  de- 
parture from  their  nominal  shape,  size,  or  cross-section. 

Paragraph  3.  Brick. — For  all  brick-work  none  but  the 
best  quality  of  sound,  hard-burned,  perfect-shaped  bricks, 
presenting  a  regular  and  smooth  surface,  shall  be  used.  After 
being  thoroughly  dried  and  immersed  in  water  for  24  hours 
they  shall  not  absorb  more  than  10  per  cent  by  weight  of 
water.  Shale  brick,  if  used,  shall  be  composed  of  rock 
thoroughly  ground  and  shall  be  homogeneous  throughout  and 
uniformly  burned. 

Paragraph  4.  Paving-stone. — This  shall  consist  of  hard 
granite  or  trap-rock,  uniform  in  grain  and  texture.  The 
blocks  must  be  rectangular  in  form,  not  less  than  3  nor  more 
than  4  inches  in  either  length  or  breadth,  nor  less  than  4  nor 
more  than  5  inches  in  depth,  and  so  split  and  dressed  with 
true  surfaces  that  on  neither  top,  ends,  nor  sides  shall  there 
be  a  projection  from  the  general  surface  exceeding  J  inch. 

(This  stone  is  used  for  inverts  where  there  is  excessive  ve- 
locity in  the  sewer  or  impact  from  falling  water.) 

Paragraph  5.  Masonry-stone. — Stone  for  foundations 
and  backing  shall  be  of  a  sound  and  durable  quality,  free  from 
cracks  and  seams,  having  top  and  bottom  beds  approximately 
parallel.  No  stone  shall  be  less  than  4  inches  thick,  12 
inches  long,  and  8  inches  wide. 

Paragraph  6.  Iron  Castings. — All  iron  castings  shall  be 
made  from  a  superior  quality  of  gray  iron,  remelted  in  the 
cupola  or  air-furnace,  tough  and  of  even  grain,  and  shall 
possess  a  tensile  strength  of  not  less  than  18,000  pounds  per 
square  inch.  Test-bars  of  the  metal  3  inches  by  £  inch,  when 


igb  SEWEKAGE. 

placed  upon  supports  1 8  inches  apart  and  loaded  in  the 
centre,  shall  have  a  transverse  breaking  load  of  not  less  than 
1000  pounds,  and  shall  have  a  total  deflection  of  not  less  than 
f  inch  before  breaking.  These  test-bars  shall  be  poured  from 
the  ladle  at  any  time  the  engineer  directs,  before  or  after  the 
castings  have  been  or  while  they  are  being  poured.  All 
castings  shall  conform  to  the  shape  and  dimensions  shown 
•upon  the  drawings  and  shall  be  clean  and  perfect,  without 
blow-  or  sand-holes  or  defects  of  any  kind.  No  plugging  or 
other  stopping  of  holes  will  be  allowed.  The  castings  shall 
be  thoroughly  cleaned  of  all  lumps  and  subjected  to  careful 
hammer  tests,  after  which  they  are  to  be  dipped  in  a  bath  of 
coal-tar  pitch  heated  to  at  least  200°  Fahr. 

Iron  pipe  shall  comply  with  the  above  specifications, 
except  that  the  engineer  may,  at  his  option,  receive  a  pipe 
having  a  limited  number  of  small  sand-  or  blow-holes  on  its 
exterior  surface.  No  portion  of  the  shell  of  the  pipe  shall 

have  a  less  thickness  than (this  thickness  can  generally  be 

made  the  least  which  will  permit  of  handling  of  the  pipe  with- 
out danger  of  breaking  it,  and  non-uniformity  of  shell  is  not 
objectionable  if  payment  is  not  made  by  weight). 

Paragraph  7.  Wrought  Iron. — All  wrought  iron  must  be 
tough,  ductile,  and  fibrous,  of  a  uniform  quality,  free  from 
crystalline  structure,  cinders,  flaws,  or  cracks.  In  bars  it 
must  have  an  ultimate  strength  of  50,000  pounds  per  square 
inch.  Iron  which  has  been  burnt  in  the  forge  will  be  rejected. 
Each  wrought-iron  piece  furnished  shall  correspond  in  all 
respects  to  the  dimensions  specified. 

Paragraph  8.  Sand. — All  sand  shall  be  clean,  sharp,  and 
free  from  loam,  clay,  or  vegetable  matter.  It  shall  not  be  so 
fine  that  each  grain  on  the  surface  of  a  pile  cannot  be  readily 
noted  with  the  naked  eye,  nor  shall  it  be  exceedingly  coarse 
when  used  for  brick  masonry. 

(Dirt  in  sand  can  usually  be  detected  by  rubbing  a  small 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.     1 97 

amount  on  the  palm,  which  will  be  soiled  by  any  clay  or  loam 
present.} 

Paragraph  9.  Cement. — Unless  otherwise  specified  all 
cement  shall  be  of  the  best  quality  of  natural  cement,  and 
when  tested  neat  in  briquettes  (Am.  Soc.  C.  E.  standard) 
shall  show  a  tensile  strength  of  at  least  75  pounds  after  I  hour 
in  air  and  23  hours  in  water  and  of  at  least  150  pounds  after 
I  day  in  air  and  6  days  in  water.  Cement  for  brick  masonry 
or  pipe-joints,  when  these  are  laid  in  wet  ground,  shall  be 
quick-setting  and  show  a  tensile  strength  of  at  least  IOO 
pounds  per  square  inch  after  24  hours.  Pats  of  neat  cement 
made  on  glass  and  brought  to  a  thin  edge  shall  show  no  checks 
after  setting  in  boiling  water. 

When  specified  Portland  cement  shall  be  used.  This  shall 
show  a  tensile  strength  of  at  least  400  pounds  per  square  inch 
in  a  7-day  test  made  as  above,  and  pats  of  the  same  shall 
show  no  checking.  The  cement  mixed  neat  and  stiff  into 
pats  J  inch  thick  shall  develop  "  initial  "  set  in  not  less  than 
20  minutes  and  <(  hard  "  set  in  not  less  than  45  minutes  after 
mixing,  except  in  the  case  of  quick-setting  cement  to  be  used 
as  specified  above. 

The  engineer  shall  be  allowed  to  test  all  cement  and  notice 
of  its  receipt  by  the  contractor  must  be  made  to  the  engineer 
at  least  48  hours  in  advance  of  its  use  upon  the  work.  Any 
cement  not  satisfactory  to  him  shall  be  at  once  removed  from 
the  work. 

Paragraph  10.  Packing. — Packing  may  consist  of  flax, 
jute,  oakum,  or  hemp,  clean  and  with  long  fibres  loosely 
twisted  into  strands. 

Paragraph  II.  Timber. — All  timber  and  planking  used 
in  cradles,  platforms,  and  foundations  shall  be  of  spruce,  or 
timber  equally  as  good,  straight,  sound,  free  from  sap,  shakes, 
large,  loose,  or  decayed  knots,  worm-holes,  or  other  imper- 
fections which  may  impair  its  strength  or  durability.  Piles 


198  SEWEKAGE. 

shall  be  of  sound,  straight,  live  spruce  or  yellow-pine  timber, 
of  lengths  specified  by  the  engineer  for  each  locality.  They 
shall  be  not  less  than  6  inches  in  diameter  at  the  smaller  end. 
The  bark  shall  be  removed  in  all  cases. 


ART.  52.     EXCAVATION. 

Paragraph  12.  Classification  of  Materials. — All  ma- 
terials excavated  shall  be  classified  as  either  earth  or  rock. 
No  material  shall  be  classified  as  rock  which  cannot  be 
removed  more  cheaply  by  drilling  and  blasting  than  by  pick- 
ing, except  that  any  boulder  measuring  •£  cubic  yard  or  more 
shall  be  so  classified,  whether  blasted  or  removed  bodily;  but 
such  boulder  shall  not  be  returned  to  the  trench  without  being 
first  broken  up. 

Paragraph  13.  Excavation  of  Trench. — The  trench  shall 
be  excavated  along  the  line  designated  by  the  engineer  and 
to  the  depth  necessary  for  laying  the  sewer  or  sub-drain  at  the 
grade  given  by  him.  In  the  case  of  pipe  sewers  it  shall  be  I  foot 
wider  at  the  bottom  than  the  outside  diameter  of  the  pipe, 
and  for  brick  sewers  as  wide  as  the  greatest  external  horizon- 
tal width  of  the  structure  to  be  placed  therein,  without  any 
undercutting  of  the  banks.  Where,  in  the  opinion  of  the 
engineer,  the  original  earth  is  sufficiently  compact  and  solid 
for  the  foundation  of  the  work  the  contractor  shall  excavate 
the  bottom  of  the  trench  to  conform  to  the  external  form  and 
dimensions  of  the  invert  or  foundation  as  ordered.  For  pipe 
sewers  the  bottom  of  the  trench  under  each  bell  shall  be  so 
hollowed  out  as  to  allow  the  body  of  the  pipe  to  have  a  bear- 
ing throughout  on  the  trench  bottom  and  permit  of  making 
the  joint.  In  case  a  trench  be  excavated  at  any  place, 
excepting  at  joints,  below  the  proper  grade  it  shall  be  refilled 
to  grade  with  sand  or  loam  thoroughly  rammed,  without 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.     1 99 

extra  compensation  unless  the  extra  excavation  was  ordered 
by  the  engineer. 

The  material  excavated  shall  be  laid  compactly  on  the 
side  of  the  trench  and  kept  trimmed  up  so  as  to  be  of  as  little 
inconvenience  as  possible  to  the  travelling  public  and  to 
adjoining  tenants.  Where  the  street  is  paved  the  paving 
shall  be  kept  separate  from  the  other  material  excavated. 
(Jt  is  generally  desirable  to  place  the  paving  material  on  the  side 
of  the  trench  whicJi  is  to  be  left  open  for  travel,  and  the  earth 
upon  the  other.)  All  streets  shall  be  kept  open  for  travel  and 
the  engineer  reserves  the  right  to  require  the  use  of  excavat- 
ing-machinery  if  necessary  to  insure  this. 

No  tunnelling  will  be  allowed  except  by  written  permit, 
with  restrictions,  from  the  engineer.  When  tunnelling,  the 
contractor  will  excavate  the  material  to  such  cross-section  as 
may  be  designated,  using  timbering  or  other  tunnel-lining  and 
shoring  satisfactory  to  the  engineer.  The  location  and  size 
of  any  shafts,  and  the  location  of  pumps,  derricks,  boilers, 
and  other  machinery,  must  be  approved  by  the  engineer  (see 
Art.  6p).  The  engineer  shall  have  the  right  to  limit  the 
amount  of  trench  which  shall  be  opened  or  partly  opened  at 
any  one  time  in  advance  of  the  completed  sewer,  and  also  the 
amount  of  trench  left  unfilled. 

The  contractor  shall  not,  without  permission  from  the 
engineer,  remove  from  the  line  of  the  work  any  sand,  gravel, 
or  earth  excavated  therefrom  which  may  be  suitable  for 
refilling  the  trench  until  the  same  shall  have  been  refilled. 

Paragraph  14.  Pumping  and  Bailing. — The  contractor 
shall  furnish  all  necessary  machinery  for  the  work,  shall 
pump,  bail,  or  otherwise  remove  any  water  which  may  be 
found  or  shall  accumulate  in  the  trenches,  and  shall  perform 
all  work  necessary  to  keep  them  clear  of  water  while  the 
foundations  and  the  masonry  are  being  constructed  or  the 
sewer  laid.  In  no  case,  unless  by  special  permission  of  the 


20O  SEWERAGE. 

engineer,  shall  water  be  allowed  to  run  over  the  invert  or 
foundation  or  through  the  sewer  until  the  cement  is  satisfac- 
torily hardened.  The  disposal  of  the  water  after  removal 
shall  be  satisfactory  to  the  engineer. 

Paragraph  15.  Shoring  and  Sheathing.  —  Whenever 
necessary  the  sides  of  the  trench  shall  be  braced  and  rendered 
secure  and  either  open  or  close  sheathing  used,  to  the  satis- 
faction of  the  engineer;  such  sheathing  and  bracing  to  be  left 
in  until  the  trench  is  refilled,  all  such  bracing  and  sheathing 
being  done  at  the  contractor's  expense.  Sheathing  left  in 
permanently  by  the  order  of  the  engineer,  and  only  such,  will 
be  paid  for  at  the  price  bid.  When  left  in  the  trench  sheath- 
ing shall  be  cut  off  at  a  point  about  I  foot  below  the  surface. 
The  contractor  shall,  at  his  own  expense,  shore  up  and  other- 
wise protect  any  building  which  may,  in  the  opinion  of  the 
engineer,  be  endangered  by  the  work. 

Paragraph  16.  Railway-crossings. — When  any  railway- 
lines  are  to  be  crossed  or  interfered  with  specific  directions 
as  to  the  time  and  manner  of  doing  this  work  will  be  given  by 
the  engineer,  and  the  contractor  shall  conform  to  such  direc- 
tions. He  shall  be  allowed  for  material  furnished  and  made 
part  of  the  permanent  construction,  so  far  as  it  may  be  addi- 
tional to  that  indicated  on  the  plan,  but  all  other  work  shall 
be  done  at  his  own  cost. 

Paragraph  17.  Interference  with  Existing  Structures 
and  Watercourses. — In  excavating  and  back-filling  trenches 
and  laying  the  sewer  care  must  be  taken  not  to  move  or  injure 
any  gas-,  water-,  sewer-,  or  other  pipes,  conduits,  or  structures 
without  the  order  of  the  engineer.  If  necessary  the  contractor 
shall,  at  his  own  expense,  sling,  shore  up,  and  secure,  and 
maintain  a  continuous  flow  in  said  structures,  and  shall  repair 
any  damage  done  to  them  and  keep  them  in  repair  until  the 
final  acceptance  of  the  completed  works,  leaving  them  in  as 
good  condition  as  when  uncovered.  Should  it  be  necessary 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.     2OI 

to  move  the  position  of  a  pipe  or  conduit  this  shall  be  done 
in  accordance  with  the  instructions  of  the  engineer,  and  the 
contractor  shall  be  allowed  for  material  furnished  and  made 
part  of  the  permanent  construction,  so  far  as  it  may  be  addi- 
tional to  that  indicated  upon  the  plans,  and  for  labor  per- 
formed on  such  additional  construction,  but  all  other  work 
shall  be  done  at  his  own  expense. 

At  such  street-crossings  and  other  points  as  may  be 
directed  by  the  engineer  the  trenches  shall  be  bridged  in  a 
secure  manner,  so  as  to  prevent  any  serious  interruption  of 
travel  upon  the  roadway  and  sidewalks  and  also  to  afford 
necessary  access  to  public  and  private  premises.  The  mate- 
rial used  and  mode  of  constructing  such  bridges  and  the 
approaches  thereto  must  be  satisfactory  to  the  engineer;  the 
cost  of  all  such  work  must  be  included  in  the  regular  price  bid 
for  the  sewer.  (Crossings  should  not  be  tunnelled  under,  since 
it  is  almost  impossible  to  so  refill  the  tunnels  as  to  prevent  after- 
settlement,  but  should  be  bridged.  Direct  access  to  the  street 
should  be  given  to  fire-engine  houses  and  usually  to  livery- 
stables.}  All  fire-hydrants  shall  be  left  uncovered  and  accessi- 
ble. The  contractor  shall  at  his  own  expense  provide  for  all 
watercourses,  gutters,  and  drains  interrupted  by  the  work, 
and  replace  them  in  as  good  condition  as  he  found  them. 

Paragraph  18.  Rock  Trenches. — When  the  excavation 
for  a  pipe  sewer  or  drain  is  made  through  rock  or  other 
material  too  hard  to  be  readily  or  conveniently  removed  for 
admitting  the  hubs  of  the  pipe  the  trench  shall  be  excavated 
at  least  4  inches  deeper  than  the  grade  of  the  outside  bottom 
of  the  pipe  and  [filled  with  concrete  up  to  and  around  such 
pipe,  as  shown  upon  the  plans]  [refilled  to  such  grade  with 
sand  or  loam,  free  from  stones  or  other  hard  substances, 
thoroughly  rammed].  When  rock  is  encountered  in  the 
trench  it  shall  be  stripped  of  earth  and  the  engineer  notified 
and  given  proper  time  to  measure  the  same  before  blasting. 


202  SEWERAGE. 

All  rock  removed  which  has  not  been  measured  by  the 
engineer  will  not  be  estimated  as  rock  excavation.  Measure- 
ment for  rock  excavation  will  be  limited  to  6  inches  on  either 
side  of  the  sewer,  and  trench-slopes  of  8  vertical  to  I  hori- 
zontal. In  all  cases  of  blasting  the  blast  shall  be  carefully 
covered  with  heavy  timbers  chained  together,  and  the  engineer 
may  limit  the  number  of  simultaneous  discharges.  Not  more 
than  30  pounds  of  dynamite  shall  be  kept  on  hand  at  one  time 
in  any  one  place.  No  blasting  shall  be  done  within  40  feet 
of  the  finished  sewer  or  10  feet  of  an  uncovered  gas-  or 
water-pipe,  and  the  end  of  the  finished  sewer  shall  be  covered 
or  stopped  with  plank  or  earth  during  each  blast.  (If  the 
sewer-end  is  not  so  protected  there  is  a  possibility  of  stones  flying 
into  the  sewer  and  also  of  the  concussion  of  air  opening  the 
joints.} 

ART.  53.     CONSTRUCTION. 

Paragraph  19.  Foundations.  —  When  timber  or  pile 
foundations  other  than  those  shown  in  the  plans  are  neces- 
sary, in  the  opinion  of  the  engineer,  special  designs  will  be 
furnished  the  contractor,  who,  in  accordance  with  such 
designs,  shall  place  such  foundations  in  position  satisfactory 
to  the  engineer.  Planking  in  platforms  shall  be  laid  in  the 
manner  directed,  closely  joined,  and  each  plank  spiked  to  each 
cap  or  sill  with  nails  or  spikes  of  a  length  at  least  2\  times  the 
thickness  of  the  plank.  If  cradles  or  platforms  are  laid 
directly  upon  the  ground  this  must  be  graded  perfectly  even 
and  smooth  to  receive  them  and  give  a  good  and  firm  bearing 
throughout.  If  caps  or  sills  are  used  the  spaces  between  them 
and  under  the  planking  must  be  filled  with  good  earth 
thoroughly  rammed. 

Where  piles  are  used  they  shall  be  driven  to  refusal,  unless 
extending  more  than  10  feet  below  the  foundation,  when  they 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.    2O3 

shall  show  a  penetration  in  inches  under  the  final  blow  not 

W/i 

greater  than  -j i,  in  which  L  is  the  weight  to  be  borne 

by  each  pile,  w  is  the  weight  of  the  hammer  in  pounds,  and 
h  its  fall  in  feet.  After  driving,  the  piles  shall  be  sawed  off 
truly  and  evenly  at  the  proper  elevation  for  receiving  the 
caps,  which  shall  be  fastened  to  them  with  i-inch  drift-bolts 
of  a  length  twice  the  depth  of  the  sill,  holes  for  such  bolts 
having  first  been  bored  with  a  £-inch  bit.  If  any  pile  shall 
be  out  of  line  more  than  \  the  diameter  of  its  upper  end  the 
engineer  may  refuse  to  estimate  it  and  may  order  another 
driven  in  its  place. 

Concrete  or  stone-masonry  foundations  shall  be  con- 
structed where  ordered  in  a  manner  similar  to  that  specified 
for  "  Concrete"  and  "  Stone  Masonry." 

Paragraph  20.  Concrete. — Concrete,  unless  otherwise 
specified,  shall  be  composed  of  I  part  by  bulk  of  natural 
cement,  3  parts  of  sand,  and  5  parts  of  broken  stone,  gravel, 
or  furnace-slag  of  approved  quality,  free  from  dust  and  dirt 
and  broken  so  as  to  pass  in  every  way  through  a  2-inch  ring. 
All  material  shall  be  actually  measured  for  each  batch,  the 
cement  compacted  in  barrels  as  received  (or,  if  received  in 
bags,  an  equivalent  quantity  as  ascertained  by  trial),  the  sand 
and  stone  in  similar  barrels  or  specially  prepared  boxes.  In 
mixing,  the  sand  shall  be  spread  out  upon  a  suitable  platform 
or  box  and  the  cement  deposited  upon  this;  these  shall  then 
be  thoroughly  mixed  dry  until  the  whole  is  of  an  even, 
uniform  color,  when  sufficient  clean  water  shall  be  added  to 
form  a  thick  paste.  The  stone,  which  has  previously  been 
thoroughly  wet,  shall  then  be  added  and  the  whole  shall  be 
quickly  and  thoroughly  mixed,  until  every  stone  is  coated 
with  mortar,  water  being  gradually  added  by  sprinkling,  if 
necessary,  to  obtain  a  better  consistency.  If  mixing  be  done 
by  machinery  it  shall  produce  a  mixture  equally  as  good  as  by 


204  SEWERAGE. 

the  above  method.  Concrete  must  not  be  mixed  in  quantities 
greater  than  required  for  immediate  use,  and  any  which  has 
begun  to  set  shall  not  be  retempered  or  used  in  any  way. 
Concrete  shall  be  deposited  in  layers  not  to  exceed  9  inches 
in  thickness,  and  settled  by  thorough  light  ramming,  sufficient 
to  bring  water  to  the  surface.  One  course  shall  follow  another 
as  rapidly  as  possible.  Where  fresh  concrete  is  to  be  placed 
in  contact  with  that  already  set  or  partly  set  all  loose  stone 
or  concrete  not  thoroughly  compacted  shall  be  removed  from 
the  surface  of  the  latter,  which  shall  be  washed  clean  of  all 
dirt  and  given  a  thin  coat  of  mortar.  If  such  a  surface  be 
hard  set  it  shall  previously  be  thoroughly  water-soaked. 
When  concrete  is  in  place  all  wheeling,  working,  or  walking 
on  it  must  be  prevented  until  it  is  firmly  set,  and  until  such 
time  it  shall  be  kept  damp  and  protected  from  the  sun. 

Such  forms  and  centres  as  may  be  necessary  to  give  the 
finished  concrete  the  desired  form  shall  be  furnished  by  the 
contractor  without  extra  charge.  These  shall  be  sufficiently 
stiff  and  substantial  to  retain  the  concrete  firmly  in  place,  and 
shall  not  be  withdrawn  until  the  same  has  set  to  the  satisfac 
tion  of  the  engineer.  No  concrete  shall  be  made  or  used 
when  the  temperature  is  below  35°  Fahr.  without  the  permis- 
sion of  the  engineer,  whose  instructions  and  restrictions  for 
such  use  shall  be  followed.  (When  an  entire  sewer  is  composed 
of  concrete  a  better  quality ',  generally  made  of  Portland  cement  > 
is  used  for  the  invert :,  and  the  inside  is  plastered.) 

Paragraph  21.  Stone  and  Brick  Masonry. — Stone  and 
brick  masonry,  unless  otherwise  specified,  shall  be  laid  with 
mortar  composed  of  I  part  by  measure  of  natural  cement  to 
2  of  sand,  mixed  as  specified  for  concrete  mortar.  No  mortar 
shall  be  used  after  it  has  set  or  partially  set. 

Stone  masonry  must  be  laid  true  and  by  line  and  built  of 
the  exact  dimensions  shown  in  the  plans  of  the  work.  All 
stones  shall  be  laid  upon  their  natural  beds  and  roughly 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.     2O$ 

squared  on  the  joints,  beds,  and  faces,  the  stone  breaking 
joints  at  least  6  inches,  and  with  at  least  one  header  for  every 
three  stretches.  Headers  shall  be  at  least  3  feet  long  or 
extend  entirely  through  the  wall.  No  stone  once  bedded 
shall  be  lifted  by  spalling,  but  any  spalls  used  must  be  em- 
bedded in  the  mortar  before  setting  the  stone.  Each  stone 
shall  be  floated  to  place  in  a  full  bed  of  mortar  and  every 
joint  thoroughly  filled  with  the  same.  No  dressing  of  stone 
upon  the  wall  will  be  allowed.  (For  river-  or  retaining- walls 
further  specifications  should  be  added  as  to  tJiickness  of  joints, 
character  of  face  dressing,  etc.} 

For  brick  masonry  in  straight  walls  or  sewers  none  but 
whole,  sound  brick  shall  be  used.  For  manholes,  flush-tanks, 
and  similar  work  a  limited  number  of  half  brick  may  be  used, 
not  to  exceed  £  of  the  whole  in  any  case.  Unless  the  engineer 
direct  otherwise  each  brick  shall  be  thoroughly  wetted  imme- 
diately before  being  laid.  (If  the  brick  absorbs  practically  no 
water  this  wetting  should  be  omitted,  as  likely  to  cause  the  brick 
to  slide  on  the  mortar  and  cause  uneven  work.)  It  shall  be  laid 
with  a  full,  close  joint  of  cement  mortar  on  its  bed,  ends,  and 
side  at  one  operation.  In  no  case  is  mortar  to  be  slushed  in 
afterward.  Special  care  shall  be  taken  to  make  the  face  of 
the  brick-work  smooth,  and  all  joints  on  the  interior  of  a 
sewer  shall  be  carefully  struck  with  the  point  of  a  trowel  or 
pointed  to  the  satisfaction  of  the  engineer.  Where  pipe- 
connections  enter  a  sewer  or  manhole  "  bull's-eyes  "  shall  be 
constructed  by  laying  rowlock  courses  of  brick  around  them, 
the  cost  of  such  construction  being  included  in  the  regular 
price  bid  for  the  sewer  or  appurtenance.  Around  pipe  more 
than  15  inches  in  diameter  2  rowlock  courses  shall  be  laid. 

Brick-work  in  sewers  shall  be  laid  by  line,  each  course 
perfectly  straight  and  parallel  to  the  axis  of  the  sewer.  Joints 
appearing  in  the  sewer  shall  in  no  case  exceed  £  inch  in  width. 
Sewers  shall  conform  accurately  in  section  and  dimensions  to 


2O6  SE  WERA  GE. 

the  plans  of  the  same.  All  inverts  and  bottom  curves  shall 
be  worked  from  templets  accurately  set,  the  arches  are  to  be 
formed  upon  strong  centres  accurately  and  solidly  set,  and  the 
crowns  keyed  in  full  joints  of  mortar.  No  centres  shall  be 
drawn  until  the  arch  masonry  has  set  to  the  satisfaction  of  the 
engineer  and  refilling  progressed  up  to  the  crown.  They 
shall  be  drawn  with  care,  so  as  not  to  crack  or  injure  the  work. 
The  extrados  is  to  be  neatly  plastered  with  cement  mortar  J 
inch  thick,  the  arches  being  cleaned  and  wetted  just  before 
plastering.  The  end  of  each  section  of  brick  sewer  shall  be 
toothed  or  racked  back,  and  before  beginning  the  succeeding 
section  all  loose  brick  at  the  end  shall  be  removed  and 
the  toothing  cleaned  of  mortar.  All  brick-work  shall  be 
thoroughly  bonded,  adjacent  courses  breaking  joints  at  least 
-J-  the  exposed  length  of  the  brick. 

Stone  blocks  shall  be  laid  in  Portland-cement  mortar  com- 
posed of  equal  parts  by  measure  of  cement  and  sand.  Joints 
shall  not  exceed  f  inch  in  width.  The  face  of  the  masonry 
shall  be  such  that  there  shall  be  no  projection  beyond  the 
general  surface  exceeding  J  inch.  All  joints  shall  be  cleaned 
out  to  a  depth  of  \  inch  and  pointed  with  neat  Portland- 
cement  mortar.  All  stone-block  work  shall  be  laid  in  other 
respects  as  specified  for  brick-work. 

If  there  should  be  any  distortion  of  the  sewer  before 
acceptance  this  shall  be  corrected  by  tearing  down  and  rebuild- 
ing. No  local  patching  will  be  allowed,  but  when  repairs  are 
necessary  a  section  shall  be  removed  at  least  3  feet  long  and 
including  the  entire  arch,  or  the  entire  sewer  if  the  defect  is 
in  the  invert.  Leakage  of  ground-water  into  the  sewer  shall 
be  similarly  corrected,  unless  it  can  be  prevented  by  calking 
the  joints  with  oakum  saturated  in  cement,  with,  wooden 
plugs,  or  other  material  acceptable  to  the  engineer. 

Paragraph  22.  Laying  Pipe  Sewers. — Previous  to  being 
lowered  into  the  trench  each  pipe  shall  be  carefully  inspected, 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.     2O/ 

and  those  not  meeting  the  foregoing  specifications  shall  be 
rejected,  and  either  destroyed  or  removed  from  the  work 
within  10  hours;  except  that  pipe  suitable  for  sub-drains  may 
be  used  for  that  purpose,  but  shall  be  kept  apart  from  the 
sewer-pipe.  All  lumps  or  excrescences  on  the  ends  of  each 
pipe  shall  be  removed  before  it  is  lowered  into  the  trench. 
No  pipe  shall  be  laid  except  in  the  presence  of  the  engineer 
or  his  authorized  inspector,  and  the  engineer  may  order  the 
removal  and  relaying  of  any  pipe  not  so  laid.  The  trench 
shall  be  excavated  in  accordance  with  Paragraphs  13  and  18. 
No  sewers  shall  be  laid  within  10  feet  of  the  excavating  or  40 
feet  of  the  blasting.  Pipes  having  any  defects  which  do  not 
cause  their  rejection  shall  be  so  laid  as  to  bring  these  in  the 
top  half  of  the  sewer,  and  if  the  bell  or  spigot  be  broken  the 
defective  place  must  be  liberally  covered  with  neat-cement 
mortar,  reinforced  with  a  piece  of  pipe  or  pipe-ring  if  the 
engineer  so  direct. 

The  pipes  and  specials  shall  be  so  laid  in  the  trench  that 
after  the  sewer  is  completed  the  interior  surface  thereof  shall 
conform  accurately  to  the  grades  and  alignment  fixed  and 
given  by  the  engineer.  All  adjustment  to  line  and  grade  of 
pipes  laid  directly  upon  the  bottom  must  be  done  by  scraping 
away  or  filling  in  the  earth  under  the  body  of  the  pipe,  and 
not  by  blocking  or  wedging  up.  Before  laying,  the  interior 
of  the  bell  shall  be  carefully  wiped  smooth  and  clean,  and  the 
annular  space  shall  be  free  from  dirt,  stones,  or  water.  [(For 
hub -and- spigot  joints.']  A  narrow  gasket  of  packing  dipped  in 
cement  grout  shall  be  properly  calked  into  each  joint,  after 
which  cement  mortar  shall  be  introduced  therein.  Such 
gasket  shall  be  in  one  piece,  of  sufficient  length  to  reach 
entirely  around  the  pipe  and  of  a  thickness  sufficient  to  bring 
the  bottoms  of  the  two  pipes  to  the  same  level.  No  joint 
shall  be  cemented  until  the  gaskets  of  the  next  two  joints  in 
advance  are  properly  inserted.  Special  care  must  be  taken 


208         '  SEWERAGE. 

to  properly  fill  with  mortar  the  annular  space  at  the  bottom 
and  sides  as  well  as  at  the  top  of  the  joints.  After  such 
space  has  been  filled,  the  cement  having  been  compacted  with 
a  wooden  or  iron  calking-tool,  a  neat  finish  shall  be  given  to 
the  joint  by  the  further  application  of  similar  mortar  to  the 
face  of  the  hub  so  as  to  form  a  continuous  and  even  bevelled 
surface  from  the  exterior  of  said  hub  to  the  exterior  of  the 
spigot  all  around.]  [(For  bevelled  joints.)  The  bevels  shall 
each  be  covered  with  a  layer  of  cement  at  least  J  inch  thick 
and  the  spigot  pipe  steadily  pushed  home  with  some  force. 
A  band  of  cement  at  least  J  inch  thick  and  3  inches  wide  shall 
then  be  neatly  wiped  around  the  outside  of  the  sewer  at  the 
joint.]  All  water  must  be  kept  out  of  the  bell-hole  during 
laying,  or  else  such  bell-hole  must  be  completely  filled  out 
with  the  cement  mortar  specified  or  with  concrete,  for  which 
mortar  or  concrete  no  extra  compensation  will  be  allowed. 
The  interior  of  the  joint  shall  be  wiped  clean  of  cement  by  a 
wad  made  of  a  sack  filled  with  hay,  large  enough  to  tightly 
fill  the  pipe  and  attached  to  a  rod  or  cord,  which  shall  at  all 
times  be  kept  in  the  sewer  and  pulled  ahead  past  each  joint 
as  soon  as  it  is  cemented.  The  mortar  used  shall  be  com- 
posed of  [i  part  cement  to  I  of  sand]  [neat  cement]  wet  to  a 
thick  paste.  (Engineers  do  not  agree  as  to  the  advisability  of 
using  neat-cement  mortar.  Experiment  seems  to  show  that 
natural  cement  gives  a  tighter. joint  if  mixed  with  sand,  Port- 
land if  used  neat.)  Natural  cement  shall  be  used  under 
ordinary  conditions,  but  the  engineer  may  require  the  use  of 
quick-setting  or  of  Portland  cement  when  he  thinks  it  neces- 
sary. 

As  soon  as  the  cementing  of  any  joint  has  been  completed 
the  bell-hole  under  the  hub  must  be  carefully  and  compactly 
filled  with  sand,  loam,  or  fine  earth,  so  as  to  hold  the  external 
mortar  finish  of  said  joint  securely  in  its  place.  Refilling 
shall  also  be  made  with  selected  material,  free  from  stones, 


'-•       SPECIFICATIONS,   CONTRACT,  ESTIMATE    OF  COST.     209 

carried  halfway  up  the  sides  or  circumference  of  the  entire 
length  of  pipe  and  compacted  with  a  proper  tamping-tool. 
The  trench  shall  then  be  filled  to  a  point  at  least  2  feet  above 
the  top  of  the  pipe  with  material  containing  no  stone  larger 
than  2  inches  in  any  dimension. 

While  the  pipes  and  specials  are  being  laid  in  each  section 
between  manholes  or  other  permanent  openings  light  from  the 
remote  end  of  the  section  shall  remain  constantly  in  plain  view 
throughout  the  entire  length  of  such  section  or  division. 
Sections  between  openings  will  in  general  not  exceed  300  to 
400  feet ;  in  particular  cases  the  distance  may  be  somewhat 
greater. 

At  such  places  as  will  be  directed  by  the  engineer,, 
branches  will  be  inserted  in  the  sewer  for  future  connections. 
Each  branch  thus  inserted  shall  be  closed  by  a  thin  vitrified 
stoneware  cover  or  plug,  which  shall  be  placed  before  the 
special  pipe  is  lowered  into  the  trench.  The  covers  shall  be 
so  inserted  and  cemented  in  as  to  prevent  any  water  entering 
the  sewer,  at  any  time  before  their  removal,  through  such 
branches.  The  entire  cost  of  furnishing  and  setting  such 
covers  shall  be  included  in  the  regular  price  bid  for  branches. 
Where  directed  by  the  engineer  deep  cut  connections  (Fig.. 
-  -  -)  shall  be  constructed  as  shown  upon  the  plans. 

Any  omission  of  the  required  branches,  manholes,  lamp- 
holes,  or  other  special  constructions  indicated  upon  the  plans,, 
or  that  may  be  specially  ordered  beforehand  by  the  engineer, 
shall  be  corrected  by  the  contractor  at  his  own  expense. 

Before  leaving  the  work  for  the  night  or  at  any  other  time' 
the  end  of  the  sewer  shall  be  securely  closed  with  a  tight- 
fitting  plug. 

Paragraph  23.  Laying  Sub-drains. — Sub-drains  shall  be 
laid  in  sub-trenches  excavated  of  the  dimensions  and  in  the 
location  shown  upon  the  plans,  and  of  such  depth  as  is  neces- 
sary to  lay  the  pipe  at  the  grade  given  by  the  engineer.  This. 


2IO  SEWERAGE. 

sub-trench  shall  be  filled  with  clean  broken  stone  or  gravel, 
not  less  than  J  inch  nor  more  than  i  inch  in  any  dimension, 
up  to  the  drain  invert;  this  broken  stone  or  gravel  being  laid 
in  by  hand  or  shovels  and  lightly  compacted,  so  that  there 
may  be  no  future  settlement.  On  this  the  drain-pipe  shall  be 
laid  accurately  to  grade,  having  first  been  inspected  and  all 
pipe  not  meeting  the  specifications  having  been  rejected.  A 
piece  of  cheese-cloth  or  similar  material  satisfactory  to  the 
engineer,  at  least  5  inches  wide  and  twice  as  long  as  the  out- 
side circumference  of  the  pipe,  shall  be  laid  on  the  broken 
stone  with  its  centre  under  the  joint  between  two  pipes;  first 
one  end  and  then  the  other  of  this  shall  be  carried  over  the 
pipes  and  under  the  opposite  side,  care  being  taken  to  keep 
the  cloth  spread  out  and  its  centre  over  the  joint.  The  pipes 
shall  be  separated  by  a  space  of  about  J  inch.  The  space 
between  the  pipes  and  the  sides  of  the  sub-trench  shall  then 
be  carefully  filled  with  broken  stone  or  gravel  as  specified 
above,  carefully  compacted,  which  material  shall  be  similarly 
placed  to  a  depth  of  6  inches  above  the  pipe.  Where  directed 
by  the  engineer  this  stone-filling  shall  be  covered  by  hemlock 
plank,  to  be  paid  for  as  "  timber  in  foundations."  If  any 
earth  or  other  material  shall  fall  into  the  sub-trench  while  the 
laying  of  stone  filling  is  proceeding,  such  material  and  the 
adjacent  stone-filling  shall  be  removed  and  clean  stone  be  put 
in  its  place. 

Where  directed  by  the  engineer  branches  shall  be  inserted 
in  the  sub-drain  for  future  connections.  These  shall  be  closed 
as  specified  for  sewer  branches,  and  the  specification  as  to  the 
omission  of  sewer  specials  shall  apply  to  sub-drain  specials 
also. 

Paragraph  24.  Regular  Appurtenances. — Manholes  of 
the  various  kinds — line,  intersection,  drop,  etc. — lamp-holes, 
flush-tanks,  inlets,  and  other  appurtenances  shall  be  built 
where  the  engineer  may  direct,  in  size,  form,  thickness,  and 


tJlN  " 

SPECIFICATIONS,   CONTRACT,  ESTIMATE   Of    COST.     211 

all  other  respects  in  accordance  with  the  plans,  but  manholes 
whose  height  exceeds  12  feet  shall  have  walls  12  inches  thick 
below  that  depth.  All  appurtenances  shall  be  brought  up 
accurately  to  the  grade  given  by  the  engineer.  Great  care 
shall  be  taken  to  make  the  channels  in  manholes  and  lamp- 
holes  conform  accurately  to  the  sewer  grade.  In  the  case  of 
pipe-sewers  split  pipe  shall  be  used  for  the  inverts  to  these 
channels  where  possible.  Where  a  curve  in  the  channel  or 
some  other  condition  prevents  this  the  channel  shall  be  formed 
of  bricks  on  edge,  set  in  Portland-cement  mortar.  Brick 
channels  shall  be  lined  with  neat  Portland-cement  mortar  J 
inch  thick,  and  the  inverts  shall  be  exactly  semi-circular  of  the 
diameter  of  the  pipes  which  they  connect.  If  these  be  of 
different  diameters  the  channel  shall  taper  uniformly  from  one 
size  to  the  other. 

Flush-tanks  and  inlets  shall  be  plastered  on  the  outside 
with  £  inch  of  cement  mortar;  and  on  the  inside  shall  be  given 
three  coats  of  thin  Portland-cement  grout,  without  sand, 
applied  with  a  brush,  each  coat  being  allowed  to  set  before 
the  next  is  applied.  (This  will  be  more  certain  to  make  a 
water-tight  construction  than  plastering  with  mortar.) 

Care  shall  be  taken  to  place  the  inlet  tops,  when  these  are 
in  the  sidewalk,  exactly  in  line  with  the  curb,  and  to  place 
the  bottoms  of  the  openings  or  the  gratings  exactly  on  the 
gutter  grade  given. 

All  manholes  and  flush-tanks  shall  be  fitted  with  steps 
similar  to  those  shown  on  the  plans,  and  spaced  15  inches 
apart  vertically.  All  tops  or  other  fittings  shall  be  set  during 
the  construction  or  at  the  completion  of  each  appurtenance, 
in  a  firm,  neat,  and  workmanlike  manner. 

All  concrete,  stone,  or  brick  masonry  shall  conform  to  the 
specifications  given  in  Paragraphs  20  and  21.  Each  appurte- 
nance shall  be  begun  within  24  hours  of  the  time  it  is  reached 


212  SEWERAGE. 

in  the  laying  of  the  sewer,  and  shall  be  completed  and  the 
excavation  closed  as  expeditiously  as  possible. 

ART.  54.     BACK-FILLING  AND  CLEANING  UP. 

Paragraph  25.  a.  Back-filling. — In  back-filling  sewer- 
trenches  loose,  fine  earth,  free  from  stones,  shall  be  used  up 
to  a  point  2  feet  above  the  sewer,  and  shall  be  thoroughly 
compacted  in  6-inch  layers  with  hand-rammers.  The  re- 
mainder of  the  trench  shall  contain  not  more  than  \  broken 
rock,  and  no  stone  of  this  shall  weigh  more  than  50  pounds. 
If  necessary  to  meet  this  requirement  the  contractor  shall 
supply  suitable  material  for  back-filling.  The  filling  of  the 
trench  above  the  level  of  2  feet  above  the  sewer  shall  be 
rammed  in  Q-inch  layers,  or,  when  directed  by  the  engineer, 
the  trenches  shall  be  water- tamped.  Water-tamping  shall  be 
done  in  each  case  as  directed  by  the  engineer.  All  back-fill- 
ing shall  be  done  by  hand  and  in  no  case  shall  scrapers  or 
ploughs  be  used.  In  back-filling  of  tunnels  or  under  railroad 
tracks  especial  care  shall  be  taken  to  thoroughly  compact  the 
material.  (The  question  of  back-filling  is  a  very  troublesome 
one.  In  most  soils,  when  the  diameter  of  the  sewer  does  not 
exceed  one  sixth  of  the  depth  of  the  trench,  all  tJie  earth 
excavated  can  be  returned  without  leaving  any  ridge  and  with- 
out any  appreciable  after-settlement.  But  this  can  be  done  only 
at  a  nsiderable  expense — from  4.  to  12  cents  for  each  cubic  yard 
of  back-filling — by  careful  ramming  or  water-tamping;  in  tough 
clay  no  way  has  yet  been  found  to  accomplish  this.  When  the 
trench  is  through  fields  or  unpaved  streets  this  extra  payment  is 
not  generally  warranted  by  the  benefits  derived;  but  through 
paved  streets  it  generally  is.  The  above  specifications  are 
similar  to  those  ordinarily  used,  but  contractors  generally 
understand  that  they  will  not  be  enforced  except  in  well-paved 
streets,  and  bid  accordingly.  It  is  preferable  to  leave  the  option 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   Of   COST.     213 

confessedly  with  the  engineer  as  to  whether  the  trench  shall  be 
tamped,  and  pay  for  the  tamping  which  is  ordered,  having  it 
well  done.  The  following  specification  is  offered  as  a  substitute, 
to  be  rigidly  enforced.) 

Paragraph  25.  b.  Back-filling. — In  back-filling  sewer- 
trenches  loose,  fine  earth,  free  from  stones,  shall  be  used  up  to 
a  point  2  feet  above  the  sewer,  and  shall  be  thoroughly  com- 
pacted in  4-inch  layers  by  hand-rammers,  there  being  two 
rammers  to  each  shoveller.  Rammers  for  this  purpose  shall 
weigh  from  4  to  6  pounds  each,  and  have  not  to  exceed  10 
square  inches  of  face.  The  remainder  of  the  trench  shall 
contain  not  more  than  one  third  broken  rock,  and  no  stone  of 
this  shall  weigh  more  than  50  pounds.  If  necessary  to  meet 
this  requirement  the  contractor  shall  supply  suitable  material 
for  back-filling.  Unless  otherwise  specified  the  trench  above 
the  level  of  2  feet  above  the  sewer  shall  be  filled  by  hand  with 
this  material  up  to  within  I  foot  of  the  surface,  and  the 
remainder  of  the  filling  shall  be  made  of  fine  material  contain- 
ing no  stone  having  any  dimension  greater  than  2  inches. 
The  filling  shall  be  crowned  above  the  trench,  having  a  height 
above  the  street  surface  of  twice  as  many  inches  as  the  top 
width  of  the  trench  in  feet,  and  neatly  rounded  off,  the  paving 
material  previously  removed,  if  any,  being  spread  evenly  over 
the  top.  After  refilling,  and  for  6  months  after  the  comple- 
tion of  this  contract,  the  contractor  shall  from  time  to  time 
refill  any  settlements  which  may  occur,  constantly  maintaining 
the  trench  in  a  neat  and  safe  condition,  and  deliver  it  over  in 
that  condition  at  the  end  of  that  time.  Hand-ramming  or 
water-tamping  shall  be  used  where  directed,  and  as  follows, 
an  additional  sum  being  paid  therefor  according  to  the  price 
bid. 

For  hand-ramming  the  earth  shall  be  spread  by  shovels  in 
4-inch  horizontal  layers  and  solidly  compacted  with  rammers 
weighing  from  6  to  8  pounds  and  having  a  face  of  not  to 


214  SEWERAGE. 

exceed  20  square  inches.  There  shall  be  two  rammers  to 
every  shoveller,  and  the  former  shall  be  of  at  least  as  great 
strength  and  efficiency  as  the  latter.  The  paving  shall  be 
restored  in  as  good  condition  as  found,  being  given  a  crown 
of  \  inch  over  the  trench,  but  not,  in  the  case  of  macadam  or 
gravel  paving,  overlapping  the  old  paving.  During  back- 
filling no  sheathing  which  is  to  be  drawn  shall  at  any  time 
extend  into  earth  which  is  being  rammed,  but  it  shall  be 
drawn  so  as  to  be  always  above,  it,  if  it  cannot  be  at  once 
entirely  removed. 

For  water-tamping  the  earth  shall  be  levelled  off  in  hori- 
zontal layers  2  feet  thick  and  flooded  with  water  until,  after 
standing  for  5  minutes,  water  shall  just  show  on  the  surface, 
when  another  layer  shall  be  thrown  in  and  flooded.  This 
shall  be  continued  up  to  within  2  feet  of  the  surface  and 
allowed  to  stand  for  a  few  hours.  The  last  2  feet  shall  then 
be  put  in  and  hand-rammed  as  specified  above,  and  the  paving 
relaid. 

No  water  shall  be  turned  into  the  trench  until  all  cement- 
work  in  sewers  and  appurtenances  shall  have  had  full  time  to 
set. 

If  a  trench  is  rammed  or  water-tamped  any  earth  which 
may  have  slipped  or  caved  from  the  bank  shall  be  thrown  out 
of  the  trench  and  the  space  refilled  and  tamped  in  the  same 
way  as  the  trench  proper,  without  extra  compensation. 

Paragraph  26.  Street  Surfaces. — In  all  paved,  macada- 
mized, or  improved  streets  generally  the  surface  of  the 
trenches  shall  be  finished  without  needless  delay,  in  the  most 
workmanlike  manner,  with  the  same  kind  of  roadway  im- 
provement that  was  removed  in  excavating  the  trench,  and 
so  that  the  underlying  courses,  as  well  as  the  finished  surface, 
shall  conform  to  the  remainder  of  the  roadway,  and  shall  in 
every  respect  be  equal  in  quality,  character,  materials,  and 
workmanship  to  the  street  improvement  existing  over  the  line 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.     21$ 

of  the  trench  immediately  previous  to  making  the  excavation. 
The  expense  of  restoring  the  pavement  or  improvement  must 
be  included  in  the  price  per  lineal  foot  of  sewer. 

Paragraph  27.  Cleaning  up. — As  soon  as  the  trench, has 
been  refilled  and  paving  replaced  all  stones,  plank,  or  other 
refuse  material  of  whatever  description  deposited  and  left  by 
the  contractor  on  the  streets  shall  be  removed  therefrom  and 
the  said  streets  restored  in  all  respects  to  the  same  condition 
as  before  the  trenching  was  commenced.  All  surplus  earth 
which  may  be  left  on  the  street  after  the  trenches  have  been 
refilled  as  specified  above  shall  be  regarded  as  the  property  of 
the  contractor,  and  must  be  removed  as  soon  as  possible  at 
his  expense. 

Paragraph  28.  Final  Inspection. — Upon  notification  by 
the  contractor  of  the  completion  of  the  work  herein  contracted 
for  the  engineer  will  carefully  inspect  all  sewers,  appurte- 
nances, and  all  other  work  done  by  the  contractor.  In  each 
stretch  of  pipe  sewer  intended  to  be  straight  light  shall  be 
visible  from  one  end  to  the  other.  Any  broken  or  cracked 
pipe  shall  be  replaced  with  sound  ones.  The  interior  of  brick 
sewers  shall  be  of  the  required  shape  and  dimensions,  sound 
and  of  a  uniform  surface.  Any  deposits  found  in  the  sewers, 
protruding  cement  or  packing,  shall  be  removed  and  the  sewer- 
bore  left  clean  and  free  through  its  entire  length.  There 
shall  be  no  appreciable  amount  of  leakage  into  any  stretch  of 
sewer.  All  underdrains  shall  discharge  water  freely  and  give 
evidence  of  having  a  clean  and  open  bore.  All  manholes, 
lamp-holes,  and  other  appurtenances  shall  be  of  the  specified 
size  and  form  and  of  a  neat  appearance,  and  their  tops  shall 
be  set  to  the  proper  grade.  In  general  the  work  shall  comply 
with  these  specifications,  and  if  found  not  to  do  so  in  any 
respect  shall  be  brought  to  the  proper  condition  by  cleaning, 
pointing,  or,  if  necessary,  excavating,  and  rebuilding,  all  at 
the  expense  of  the  contractor.  But  if  it  be  found  after 


2l6  SEWERAGE. 

uncovering  any  pipe  or  other  work  at  the  order  of  the 
•engineer  that  no  defect  exists,  or  that  the  defect  was  not  due 
to  any  fault  of  the  contractor,  then  the  expense  of  this  shall 
be  borne  by  the  city. 

ART.  55.     GENERAL  PROVISIONS,  PAYMENTS,  ETC. 

Paragraph  29.  General  Provisions. — If  any  alterations 
in  plan  directed  by  the  engineer  diminish  the  quantity  of 
work  to  be  done  they  shall  not  constitute  a  claim  for  damages 
nor  for  anticipated  profits,  and  any  increase  or  decrease  shall 
be  paid  for  or  deducted  according  to  the  quantity  actually 
done,  and  at  the  price  established  for  such  work  under  this 
contract. 

The  work  .shall  be  prosecuted  in  such  manner  and  from  as 
many  different  points,  at  such  times  and  with  such  force  as 
the  engineer  may,  from  time  to  time  during  the  progress  of 
ihe  work,  determine. 

The  contractor  will  be  furnished  with  a  set  of  drawings 
showing  the  details  and  dimensions  necessary  to  carry  out  the 
work,  dimensions  in  figures  thereon  having  precedence  over 
the  scale.  These  plans  and  a  copy  of  these  specifications  are 
to  be  kept  constantly  at  the  work  by  the  contractor  or  his 
authorized  foreman.  The  plans  submitted  to  contractors  for 
proposals  are  to  be  interpreted  in  conjunction  with  the  speci- 
fications, and  descriptions  of  the  character  of  the  work  appear- 
ing on  the  plans  are  made  a  part  of  these  specifications.  No 
deviations  from  the  drawings  will  be  allowed  without  the 
direction  of  the  engineer  to  that  effect. 

Should  it  be  necessary  at  any  time  to  move  monument- 
stones  or  other  permanent  records  the  contractor  shall  not 
disturb  them  until  given  permission  by  the  engineer. 

The  contractor  shall  provide  suitable  stakes,  plank,  and 
forms,  and  render  such  assistance  to  the  engineer,  at  his  own 


SPECIFICATIONS,  CONTRACT,  ESTIMATE   OF  COST.     2 1/ 

expense,  as  may  be  necessary  to  establish  lines  and  grades  for 
the  guidance  of  his  work,  and  shall  carefully  preserve  said 
points  at  all  times. 

If  any  person  employed  by  the  contractor  on  this  work 
shall  appear  to  be  incompetent  or  disorderly  he  shall  be  dis- 
charged immediately  on  the  requisition  of  the  engineer,  and 
such  person  shall  not  again  be  employed  on  the  work. 

Paragraph  30.  Responsibility  for  Injuries. — The  con- 
tractor shall  be  responsible  for  injuries  to  person  and  property 
inflicted  during  the  prosecution  of  the  work,  and  for  all 
damages  caused  by  the  negligence  of  the  contractor  or  any  of 
his  employees,  workmen,  or  servants,  and  the  city  may  at  its 
discretion  withhold  the  amount  of  such  injury  or  damage  from 
any  estimate  due  him  which  may  be  needed  to  make  good 
such  damages  or  injuries,  and  the  city  shall  not  in  any  wise 
be  liable  therefor. 

The  contractor  shall  place  sufficient  lights  on  or  near  the 
work  and  keep  them  burning  from  twilight  to  sunrise,  shall 
erect  suitable  railing  or  protection  about  the  open  trenches, 
and  provide  all  necessary  watchmen  on  the  work  by  day  or 
night,  for  the  safety  of  the  public. 

Paragraph  31.  Imperfect  Work. — When  any  work  or 
material  is  found  to  be  imperfect,  whether  passed  upon  or  not 
by  the  inspector,  the  said  work  shall  be  taken  up  and  replaced 
by  new  work  at  any  time  prior  to  final  acceptance. 

If  the  contractor  shall  be  notified  by  the  engineer  of  any 
requirements  or  precautions  neglected  or  omitted,  or  of  any 
work  improperly  constructed,  he  shall  at  once  remedy  the 
same,  and  if  he  fail  so  to  do  the  engineer,  under  the  direction 
of  the  city,  shall  perform  such  work  at  the  contractor's 
expense  and  deduct  the  same  from  amounts  due  or  to  become 
due  the  contractor. 

Paragraph  32.  Unnecessary  Delays. — In  case  of  any 
unnecessary  delay,  in  the  opinion  of  the  engineer,  he  shall 


2l8  SEWERAGE. 

notify  the  contractor  in  writing  to  that  effect.  If  the  con- 
tractor should  not,  within  5  days  thereafter,  take  such 
measures  as  will,  in  the  judgment  of  the  engineer,  insure  the 
satisfactory  completion  of  the  work  the  engineer  may  then, 
under  authority  from  the  city,  notify  the  aforesaid  contractor 
to  discontinue  all  work  under  this  contract,  and  it  is  hereby 
agreed  that  the  contractor  is  to  immediately  respect  said 
notice  and  stop  work  and  cease  to  have  any  rights  to  posses- 
sion of  the  ground.  The  engineer  shall  thereupon  have  the 
power  to  place  such  and  so  many  persons  as  he  may  deem 
advisable,  by  contract  or  otherwise,  to  work  at  and  complete 
the  work  herein  described,  and  to  use  such  materials  as  he 
shall  find  upon  the  line  of  said  work,  or  to  procure  other 
materials  for  the  completion  of  the  same,  and  to  charge  the 
expense  of  said  labor  and  materials  to  the  aforesaid  contrac- 
tor; and  the  expense  so  charged  shall  be  deducted  and  paid 
by  the  party  of  the  first  part  out  of  such  money  as  may  be 
then  due,  or  at  any  time  thereafter  become  due,  to  said  con- 
tractor under  and  by  virtue  of  this  agreement  or  any  part 
thereof;  and  in  case  such  expense  is  less  than  the  sum  which 
would  have  been  payable  under  this  contract  if  the  same  had 
been  completed  by  the  party  of  the  second  part  [he]  [they] 
shall  be  entitled  to  receive  the  difference,  and  in  case  such 
expense  is  greater  the  party  of  the  second  part  shall  pay  the 
amount  of  such  excess  so  due. 

Paragraph  33.  Extra  Work. — If  any  work  of  the  general 
nature  of  the  work  herein  contracted  for,  but  for  doing  which 
a  bid  has  not  been  especially  made,  shall  need  to  be  done  the 
contractor  shall  do  the  same  under  the  direction  of  the 
engineer,  and  shall  receive  therefor  the  actual  cost  of  labor 
and  material  used  plus  ten  per  cent  (io#)  for  superintendence 
and  use  of  tools,  but  he  shall  not  be  entitled  to  receive  pay- 
ment for  any  work  as  extra  work  unless  ordered  by  the 
engineer  to  do  the  same  as  such.  No  claim  for  extra  work 


SPECIFICATIONS,   CONTRACT,   ESTIMATE   OF  COST.     21$ 

will  be  allowed  if  not  made  before  the  payment  of  the  next 
following  monthly  estimate. 

Paragraph  34.  Time  of  Commencement  and  Completion. 
— The  party  of  the  second  part  agrees  to  begin  the  work 
herein  contracted  for  within  two  weeks  of  the  awarding  of  the 
contract,  and  to  fully  complete  the  work  herein  specified  on 

or  before  the day  after  the  awarding  of  said  contract, 

but  the  party  of  the  first  part  may  extend  the  time  of  com- 
pletion should  they  deem  it  for  the  best  interest  of  the  city. 
[It  is  expressly  understood  that  the  party  of  the  second  part 
agrees  to  pay  all  expenses,  such  as  engineering  and  inspec- 
tion, that  the  city  may  be  put  to  by  reason  of  the  work  being 
incompleted  at  the  time  specified  in  the  contract.]  [For  each 
day  after  the  time  specified  that  the  contract  remains  un- 
completed $25  will  be  deducted  from  the  amount  due  the 
contractor,  and  for  each  day  by  which  the  contract  is  com- 
pleted previous  to  the  time  specified  the  contractor  shall  be 
entitled  to  a  bonus  of  $25.]  [For  each  day  after  the  time 
specified  that  the  contract  remains  uncompleted  $25  will 
be  deducted  from  the  amount  due  the  contractor,  and  it 
is  hereby  expressly  understood  that  said  sum  shall  be  deemed 
and  taken  in  all  courts  to  be  the  liquidated  damages  for  the 
non-performance  of  the  work  in  the  manner  aforesaid,  and  not 
in  the  nature  of  a  penalty.] 

Paragraph  35.  Definitions. — Whenever  the  word  "  en- 
gineer "  is  used  in  the  specifications  it  refers  to  the  engineer 
in  charge  of  the  work  and  also  to  his  authorized  agents. 

The  "  party  of  the  first  part  "  is  the  city  by  and  for  which 
the  work  herein  described  and  referred  to  is  being  done,  and 
the  "  party  of  the  second  part  "  is  the  person  or  persons  con- 
tracting to  do  said  work. 

The  word  "  sewer  "  in  its  general  sense  in  these  specifica- 
tions refers  to  the  sewer-barrel  and  to  any  bends,  slants, 
branches,  or  other  details  joined  to  or  forming  a  part  thereof. 


220  SEWERAGE. 

The  word  "appurtenance"  refers  to  all  manholes,  lamp- 
holes,  flush-tanks,  inlets,  and  all  structures  forming  a  part  of 
the  sewerage  system,  but  not  included  in  the  term  "  sewer." 

Paragraph  36.  Position  of  the  Engineer. — The  engineer 
shall  have  the  final  decision  on  all  matters  of  dispute  involving 
the  character  of  the  work,  the  compensation  to  be  made 
therefor,  or  any  question  arising  under  this  contract.  He 
shall,  as  representing  the  city,  have  the  option  of  making  any 
changes  in  the  line,  grade,  plan,  form,  position,  dimensions, 
or  material  of  the  work  herein  contemplated,  either  before  or 
after  construction  is  begun,  and  all  explanations  or  directions 
necessary  for  carrying  out  and  completing  satisfactorily  the 
different  descriptions  of  work  contemplated  and  provided  for 
under  this  contract  will  be  given  by  said  engineer. 

Paragraph  37.  Duties  of  the  Contractor. — The  contrac- 
tor must  perform  the  work  contracted  for  strictly  according  to 
these  specifications,  and  follow  at  all  times,  without  delay,  all 
orders  and  instructions  of  the  engineer  in  the  prosecution  and 
completion  of  the  work  and  every  part  thereof,  and  constantly 
be  on  the  ground  or  be  represented  by  a  duly  qualified  person 
to  look  after  the  work  and  receive  instructions. 

Paragraph  38.  Measurements  and  Payments. — Meas- 
urements of  sewers  and  drains  shall  be  taken  from  the  centre 
of  the  uppermost  manhole  or  flush-tank  on  each  line  to  the 
centre  of  the  manhole  at  its  junction  with  a  main  or  lateral, 
or  to  the  centre  line  of  such  main  or  lateral  at  the  junction, 
including  all  branches,  manholes,  or  other  appurtenances 
along  the  line.  The  depth  by  which  sewer  prices  will  be 
graded  will  be  measured  from  the  surface  of  the  ground  to  the 
under  side  of  the  sewer-pipe  or  masonry  or  of  the  timber 
platforms  or  foundation-sills.  The  price  bid  for  sewers  or 
drains  shall  include  furnishing  all  material  and  labor  for 
excavating,  shoring,  constructing  the  sewer  or  drain  in 
accordance  with  the  specifications  and  plans,  back-filling, 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.     221 

restoring  the  street-surface  as  previously  specified,  and  for  all 
matters  in  connection  therewith  heretofore  specified  as  being 
so  included.  Measurements  of  connections  shall  be  taken 
from  the  outside  (bell)  end  of  the  branch  to  the  upper  end  of 
the  connection-pipe.  Branches  shall  be  paid  for  by  the  piece 
at  the  price  bid,  which  shall  include  the  cost  of  furnishing  and 
fixing  plugs  in  said  branches  where  necessary. 

Deep-cut  connections  shall  be  paid  for  at  the  prices  bid 
for  "  deep-cut  connections,"  "  pipe,"  "  concrete,"  and 
11  timber  in  foundations,"  according  to  the  actual  quantities 
used,  the  bid  for  "deep-cut  connections"  including  the 
combining  of  these  and  the  setting  of,  and  extra  care  in  back- 
filling around,  the  pipe. 

Flush-tanks  shall  be  paid  for  at  the  price  bid  for  each  par- 
ticular size  of  tank,  this  to  include  the  tank  complete  as  set 
forth  in  the  drawings  and  specifications,  including  the  excava- 
tion and  back-filling,  ventilation-pipe  and  iron  head. 

Ordinary  manholes  and  lamp-holes  shall  be  paid  for  on  the 
basis  of  a  depth  of  8  feet,  with  an  additional  amount  for  each 
foot  by  which  the  depth  exceeds  8  feet,  the  price  bid  to 
include  excavating  and  back-filling,  furnishing  and  setting  iron 
castings  and  steps,  and  completing  the  whole  as  set  forth  in 
the  plans  and  specifications.  The  depth  of  flush-tanks,  man- 
holes, and  lamp-holes  shall  be  measured  from  the  invert  of  a 
pipe  sewer,  or  the  springing  of  a  brick  sewer,  to  the  top  of 
the  iron  head  when  properly  set. 

The  price  bid  for"  crossing-"  and  "  drop-manholes  "  shall 
be  an  additional  sum  over  and  above  the  bid  for  the  same  as 
a  regular  manhole,  and  shall  be  held  to  cover  furnishing 
material  for  and  constructing  the  crossing  or  drop  device  as 
shown  in  the  plans,  as  an  addition  to  the  regular  manhole. 
The  bid  for  the  crossing-manhole  shall  be  a  lump  sum;  that 
for  the  drop-manhole  shall  be  per  vertical  foot,  measuring 
from  the  invert  of  the  lower  to  that  of  the  upper  sewer. 


222  SEWERAGE. 

The  price  bid  for  inlets,  catch-basins,  and  other  appurte- 
nances shall  include  the  excavation  and  back-filling,  and  fur- 
nishing all  materials  and  constructing  each  appurtenance  in 
strict  conformity  to  the  plans  and  specifications. 

The  price  bid  for  stone  paving  shall  be  per  square  foot, 
and  shall  be  over  and  above  the  price  for  the  sewer  or  man- 
hole in  which  it  is  laid. 

The  price  for  stone,  brick,  or  concrete  masonry  not  other- 
wise provided  for  shall  be  per  cubic  yard  by  actual  measure- 
ment in  place,  provided  such  dimensions  do  not  exceed  those 
indicated  or  implied  in  the  plans  or  instructions  of  the 
engineer. 

Iron-work,  both  cast  and  wrought,  shall  be  paid  for  by  the 
pound,  but  no  payment  for  iron-work  as  such  shall  be  made 
for  the  heads  or  steps  or  other  devices  included  in  the  man- 
holes and  other  appurtenances  as  shown  in  the  plans  and  speci- 
fications. Cast-iron  pipe  will  be  paid  for  at  the  price  per  foot 
bid  for  the  same. 

The  price  for  timber  in  foundations  shall  include  the  fur- 
nishing and  setting  of  the  same.  The  price  bid  for  furnishing 
piles  shall  be  for  the  lengths  actually  delivered,  where  these 
do  not  exceed  those  ordered  by  the  engineer.  The  price  for 
driving  piles  shall  be  per  foot,  measured  from  the  bottom  of 
the  pile  when  driven  to  the  surface  of  the  ground  in  which  it 
is  driven,  and  shall  include  cutting  off  the  piles  at  the  eleva- 
tion given  by  the  engineer. 

The  price  bid  for  tamping  trenches  shall  be  by  the  cubic 
yard  of  trench  above  a  point  2  feet  above  the  top  of  the 
sewer,  the  bottom  width  heretofore  specified  being  allowed 
and  side  slopes  of  I  in  15  in  earth  and  I  in  8  in  rock. 

The  engineer  on  the  first  of  each  month,  or  within  5  days 
thereafter,  during  construction,  will  estimate  approximately 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.     22$ 

the  amount  of  work  completed  during  the  preceding  month, 
according  to  these  specifications,  and  eighty-five  per  cent 
(85$)  of  the  amount  due  beyond  the  reservations  herein  made 
will  be  paid  the  contractor  on  or  before  the  i$th  day  of  each 
month  for  the  work  of  the  preceding  month. 

When  the  contract  shall  have  been  completely  performed 
on  the  part  of  the  contractor  the  engineer  shall  proceed  to 
make  final  measurements  and  estimates  of  the  same,  and  shall 

certify  the  same  to  the  city ,  who  shall,  except  for 

cause  herein  specified,  pay  to  the  contractor,  on  or  before  the 
1 5th  day  after  such  completion  of  the  contract,  the  balance 
which  shall  be  found  due,  excepting  therefrom  such  sum  as 
may  be  lawfully  retained  under  any  provision  of  this  contract. 

ART.  56.     CONTRACT. 

Accompanying  the  specifications  and  bound  with  them  should 
be  the  contract  proper,  of  which  a  form  is  given  : 

THIS  AGREEMENT,  made  and  concluded  the 

day  of in  the  year  One  Thousand  Eight  Hundred 

and ,  by  and  between  the  City  of , 

of  the  first  part,  and ,  Contractor,  of  the 

second  part, 

WlTNESSETH,  That  the  said  party  of  the  second  part  (has) 
(have)  agreed,  and  by  these  presents  (does)  (do)  agree  with 
the  said  party  of  the  first  part,  for  the  considerations  herein 
mentioned  and  contained,  and  under  the  penalty  expressed 
in  a  bond  bearing  even  date  with  these  presents  and  hereto 
attached,  to  furnish  at  (his)  (their)  own  proper  cost  and 
expense  all  the  necessary  material  and  labor,  except  as  herein 
specially  provided,  and  to  excavate  for  and  build,  in  a  good, 
firm,  and  substantial  manner,  the  sewers  indicated  on  the 
plans  now  on  file  in  the  office  of  the  city  engineer,  and  the 


224  SEWERAGE. 

connections  and  appurtenances  of  every  kind  complete,  of  the 
dimensions,  in  the  manner,  and  under  the  conditions  herein 
specified ;  and  (has)  (have)  further  agreed  that  the  engineer  in 
charge  of  the  work  shall  be  and  is  hereby  authorized  to 
inspect  or  cause  to  be  inspected  the  materials  to  be  furnished 
and  the  work  to  be  done  under  this  agreement,  and  to  see 
that  the  same  correspond  with  the  specifications. 

The  party  of  the  second  part  hereby  further  agrees  that 
(he)  (they)  will  furnish  the  city  with  satisfactory  evidence  that 
all  persons  who  have  done  work  or  furnished  material  under 
this  agreement,  and  are  entitled  to  a  lien  therefor  under  any 

law  of  the  State  of ,  have  been  fully  paid  or  are 

no  longer  entitled  to  such  lien,  and  in  case  such  evidence  be 
not  furnished  as  aforesaid  such  amount  as  the  party  of  the 
first  part  may  consider  necessary  to  meet  the  lawful  claims  of 
the  persons  aforesaid  shall  be  retained  from  the  moneys  due 
the  said  party  of  the  second  part,  under  this  agreement,  until 
the  liabilities  aforesaid  may  be  fully  discharged  and  the  evi- 
dence thereof  furnished. 

The  said  party  of  the  second  part  further  agrees  that  (he) 
(they)  will  execute  a  bond  in  a  sum  equal  to  25  per  cent  of 
the  contract  price,  secured  by  a  responsible  Indemnity  or 
Guarantee  Company  of,  or  authorized  by  law  to  do  business 

in,  the  State  of and  satisfactory  to  the  city,  or  by 

at  least  three  responsible  freeholders  of County 

satisfactory  to  the  city,  for  the  faithful  performance  of  this 
contract,  conditioned  to  indemnify  and  save  harmless  the  said 
city,  its  officers  or  agents,  from  all  suits  or  actions  of  every 
name  or  description  brought  against  any  of  them  for  or  on 
account  of  any  injuries  or  damages  received  or  sustained  by 
any  party  or  parties,  by  or  from  the  said  party  of  the  second 
part,  (his)  (their)  servants  or  agents,  in  the  construction  of 
said  work,  or  by  or  in  consequence  of  any  negligence  in  guard- 
ing the  same  or  any  improper  materials  used  in  its  construe- 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.     225 

tion,  or  by  or  on  account  of  any  act  or  omission  of  the  said 
party  of  the  second  part,  or  (his)  (their)  agents,  in  the  per- 
formance of  this  agreement  and  for  the  faithful  performance 
of  this  contract  in  all  respects  by  the  party  of  the  second  part ; 
and  the  said  party  of  the  second  part  hereby  further  agrees 
that  so  much  of  the  moneys  due  to  (him)  (them),  under  and 
by  virtue  of  this  agreement,  as  shall  be  considered  necessary 
by  the  said  city  may  be  retained  by  the  said  party  of  the  first 
part,  until  all  such  suits  or  claims  for  damages  as  aforesaid 
shall  have  been  settled  and  evidence  to  that  effect  furnished 
to  the  satisfaction  of  said  city. 

The  said  party  of  the  second  part  hereby  agrees  to  receive 
the  following  prices  as  full  compensation  for  furnishing  all 
materials,  labor,  and  tools  used  in  building  and  constructing,, 
excavating  and  back-filling,  and  in  all  respects  completing  the 
aforesaid  work  and  appurtenances,  in  the  manner  and  under 
the  conditions  before  specified,  and  as  full  compensation  for 
all  loss  or  damages  arising  out  of  the  nature  of  the  work  afore- 
said, or  from  the  action  of  the  elements  or  from  any  unfore- 
seen obstructions  or  difficulties  which  may  be  encountered  in 
the  prosecution  of  the  same,  and  for  all  expenses  incurred  by 
or  in  consequence  of  the  suspension  or  discontinuance  of  the 
said  work,  and  for  well  and  faithfully  completing  the  same  and 
the  whole  thereof  according  to  the  specifications  and  require- 
ments of  the  engineer  under  them,  to  wit: 

(Insert  here  spaces  for  making  bids,  being  careful  to  include 
every  item  for  which  bids  are  invited.  As  an  example:} 

For  all  36-inch  brick  sewer,   trenches 

from  6  to  8  feet  deep $ per  lineal  foot 

For  water-tamping per  cubic  yard 

For  each  manhole  8  feet  deep,  complete      

For  each  vertical  foot  of  manhole  more 

than  8  feet  deep,  8-inch  wall 


226  SE  WERA  G  E. 

For  each  vertical  foot  of  manhole  more 

than  8  feet  deep,  12-inch  wall 

For  timber  foundations per  M  B.  M. 

etc.     etc. 

And  the  said  party  of  the  second  part  further  agrees  that 
(he)  (they)  will  not  assign,  transfer,  or  sublet  the  aforesaid 
work,  or  any  part  thereof  without  the  written  consent  of  the 
city,  and  that  any  assignment,  transfer,  or  subletting  without 
the  written  consent  aforesaid  shall  in  every  case  be  absolutely 
void. 

IN  WITNESS  WHEREOF  the  said  party  of  the  second  part 
(has)  (have)  hereunto  set  (his)  (their)  hand  and  seal  and  the 
said  party  of  the  first  part  has  caused  these  presents  to  be 

sealed  with  its  common  seal  and  to  be  signed  by  the .„ 

on  the  day  and  year  above  written. 


It  is  recommended  that  the  engineer  refer  to  Johnson's 
<4  Contracts  and  Specifications,"  where  will  be  found  a  full 
discussion  of  the  subject  from  both  the  legal  and  engineering 
standpoint. 

ART.  57.     ESTIMATE  OF  COST. 

It  is  generally  desirable,  and  frequently  required  by  law, 
that  a  careful  estimate  be  made  of  the  cost  of  the  work  to  be 
done.  For  this  purpose  map,  plans,  specifications,  and  profile 
should  be  carefully  studied  to  obtain  quantities,  and  the 
amount  of  rock  to  be  excavated,  quicksand,  and  ground-water 
ascertained,  and  in  general  as  careful  a  study  made  of  the 
conditions  as  a  contractor  would  make  before  bidding.  Also 
the  prices  of  materials  should  be  obtained,  including  the  cost 
of  getting  them  upon  the  ground,  and  from  these  as  close  an 
estimate  made  as  possible  of  the  actual  cost  of  constructing 
the  system.  To  this  should  be  added  10  to  100  per  cent  for 


SPECIFICATIONS.   CONTRACT,  ESTIMATE   OF  COST.     22  / 


profit  and  contingencies,  the  latter  amount  when  the  work  is 
to  be  done  under  great  risks  and  subject  to  possible  losses. 

Out  of  a  dozen  bids  made  on  one  sewer  contract  there  are 
generally  one  or  two  quite  low,  two  or  three  others  quite  high, 
and  the  remainder  more  or  less  close  together  midway  between 
these,  and  usually  representing  a  fair  price  for  the  work,  which 
also  the  engineer's  estimate  should  do.  The  estimate  should 
not  be  too  low,  as  this  often  gives  rise  to  suspicion  of  inten- 
tional deception,  and  if  made  the  basis  of  an  appropriation  of 
funds  for  construction  may  lead  to  a  forced  curtailment  of  the 
amount  of  work  done.  On  the  other  hand,  an  unduly  high 
estimate  may  discourage  any  appropriation  whatever.  Prob- 
ably no  act  of  the  sewerage  engineer  is  more  readily  appre- 
ciated by  the  public  at  large  than  the  making  of  an  estimate 
closely  approximating  the  actual  cost. 

The  cost  of  brick,  lumber,  and  sand  varies  with  each 
locality  and  should  be  obtained  from  local  dealers.  That  of 
cement  and  pipe  varies  little  except  with  the  freight,  and  this 
variation  is  slight  between  different  places  in  the  same  section 
and  on  main  freight-lines. 

A  schedule  price  has  been  adopted  by  all  sewer-pipe 
makers,  from  which  large  discounts  are  allowed.  Such  a  list 
is  given  below.  The  discount  allowed  contractors  for  car-load 
lots  at  present  (18,98)  near  New  York  City  is  about  80  to  82 
per  cent  for  sizes  under  24  inches. 

TABLE  No.  17. 

LIST    PRICES    OF    VITRIFIED    CLAY    SEWER-PIPE,  AND  WEIGHTS     OF 
STANDARD    PIPE. 


2 

3 

0.16 
0.50 
0.72 
1.50 

7 

4 

5 

6 

8 

0-45 
i.  80 
2.03 

5-50 

22 

9 

IO 

12 

»5 

1-25 

4-75 
5-63 

63 

18 

1.70 
6.50 
7.65 

84 

20 

2.25 
7-5° 
10.13 

98 

24 

3«2S 

11.00 

14.63 
130 

Straight  pipe,  per  foot  
Bends  
Branches,  2  feet  long,  each.... 
Traps,   each  
Weight  of   straight  pipes  per 

0.14 
0.40 
0.63 

1.  00 

6 

o  20 
0.65 
0.90 

2.OO 
10 

0.25 
0.85 

1-13 
2-50 

12 

0.30 

I  .  IO 

i-35 
3-5° 

16 

0.55 
2.25 
2.48 
6.50 

26 

0.65 
2-75 
2-93 
7-5° 

32 

0.85 
3-50 
3.83 
IO.OO 

45 

Slants  are  charged  50  per  cent  more  than  plain  pipe,  and 


228 


SEWERAGE. 


measured  on  the  long  side  of  the  slant,  but  none  less  than  12 
inches  long. 

Each  additional  branch  or  trap  is  charged  branch  price. 

Double-strength  pipe  is  allowed  10  per  cent  less  discount 
than  standard  pipe. 

Increasers  are  pipe  with  the  hub  on  the  small  end  and 
reducers  with  the  hub  on  the  large  end,  and  are  charged 
double  the  price  of  2  feet  of  pipe  of  the  size  of  the  large  end. 

Channel  or  split  pipe,  which  is  pipe  cut  in  two  or  more 
pieces  lengthwise,  costs  |  the  price  of  whole  pipe. 

Stoppers  or  plugs  for  closing  pipe  cost  \  as  much  as  I  foot 
of  pipe  of  the  size  in  which  they  are  used. 

TABLE  No.  18. 

LIST    PRICES    OF    DRAIN-TILE. 


2 

2i 

•2 

4 

c 

6 

8 

10 

12 

Price,  straight  pipe  

.012 

.015 

.O2O 

.030 

.040 

•055 

.080 

.140 

.200 

36-  and  38-inch  WOODEN-STAVE  PIPE  in  Los  Angeles, 
CaL,  cost  $2.25  to  $2.50  per  foot,  complete. 

Light-weight  CAST-IRON  PIPE,  first  quality,  cost  in  1898 
about  as  follows: 


TABLE  No.  19. 

COST    OF    LIGHT    IRON    PIPE. 


Size,  inches  .  .  . 
Cost  per  foot  .  . 

.18 

6 
.27 

Q 

•35 

10 

.41 

12  1    14 
.49)    .60 

16 

•75 

18 

1.  00 

20 
1.25 

22 
1.40 

24 
1.62 

27 
1.82 

30     33 
2.20)2.50 

One  barrel  of  cement,  used  neat,  should  lay  the  following 
lengths  of  sewer,  pipes  3  feet  long: 

TABLE  No.  20. 

LENGTHS    OF    PIPE    SEWER    ONE    BARREL    OF    CEMENT    WILL    LAY. 


Size,  inches.  .. 
Length,  feet  .. 

4 
500 

6 
350 

8 

200 

9 

175 

10 

150 

12 
IOO 

15 

75 

18 
65 

20 

60 

24 

50 

The  following  gives  approximately  the  lowest  practicable 
cost    of    excavating    trenches   in   compact   loam   or    material 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.     229 


excavated  with  equal  ease.  The  prices  for  shoring  and 
sheathing  are  to  be  added  where  necessary.  These  are  based 
on  continuous  work  with  gangs  of  the  most  economical  size. 
House-connections  or  other  short  lines  would  cost  more. 
Profit  is  not  included. 

TABLE  No.  21. 

COST    OF    EXCAVATING    AND    BACK-FILLING    AND    OF    SHEATHING 

TRENCHES. 

(Compact  Loam  ;  No  Ground-water  ;  No  Machinery.) 


6 

8 

16 

18 

O7C 

IO 

14 

.20 

,2* 

o-i 

•2Q 

.  52 

OQ 

125 

.175 

.24 

.qic 

an 

•  4Q 

.65 

.  105 

.1C 

.21 

.2Q 

.38 

.465 

.585 

.78 

2          ,,            tc 

12 

I  75 

245 

^4 

je 

C  1  C 

685 

QI 

<,0      « 

14 

2O 

28 

•2Q 

CQ 

62 

78 

I  O4 

Close             j  Lumber,  @  $10. 
sheathing.  [  Setting  

•34 
08 

.42 
OQ 

•51 

II 

.64 

ia 

.80 
2O 

.92 

22 

1.  06 
24 

1.22 

26 

If  used  i\  times  *  

22 

26 

.•72 

18 

.50 

58 

66 

.7  = 

If  sheathing-planks4  feet  apart 

.10 

.12 

.15 

.18 

.24 

.27 

•30 

-33 

*  f  used  the  second  time,  i  the  third  time, 
may  be  used  an  average  of  five  times. 


the  fourth  time.     With  care  good  sheathing 


QUICKSAND  may  cost  from  two  to  ten  times  the  above. 
No  estimate  can  be  given  for  it.  ROCK  EXCAVATION  in  sewer- 
trenches  usually  costs  from  75  cents  to  $2  per  cubic  yard. 
The  greater  the  amount  of  rock  per  running  foot  to  be 
excavated  the  more  cheaply  it  can  be  done. 

The  approximate  cost  of  laying  sewer-pipe,  including  all 
but  the  excavation,  is  given  in  the  following  table: 

TABLE  No.  22. 

COST    OF    LAYING    SEWER-PIPE,    CENTS    PER    LINEAL    FOOT. 


2-foOt 

Lengths. 

3-foot  Lengths. 

4 

5 

6 

8 

9 

TO 

12 

15 

18 

20 

24 

27 

30 

33 

36 

5-25 

6.80 

4-57 
16.6-2 

Unloading,  hauling, 
and  distributing.* 
Laying,  cost  of  jute, 
calking  

0.15 

1.23 
0.44 
i.R? 

0.18 

1.38 
0.50 

•?,  ofi 

O.2I 

'•55 
o.55 

2.31 

o-35 

1.62 

0.58 

2.  Sq 

0.38 

..78 

0.65 

7.8T 

0.41 

1.97 
0-75 
3.n 

0.63 
2.31 

°-93 
7.87 

0.90 

2.58 
i.  ii 

d.SQ 

i.  20 

3.00 

1-32 

=;.=;2 

1.50 
3-70 

*.% 

2.10 

4-5° 
2.00 

8.60 

3-00 
5.06 

2-35 

10.41 

4.00 

5.48 
2.90 
12    38 

4.46 

6.00 
3.86 

14.32 

Cement,  mixed  
Total  .  .  , 

*  Teams  hauling  4500  pounds  per  load;  average  haul  one  mile;  $3.50  per  day. 


2  30 


SEWERAGE. 


The  approximate  cost  of  building  circular  brick  sewers  is 
given  in  the  following  table.  This  does  not  include  excava- 
tion or  back-filling. 

TABLE  No.  23. 

COST    OF    CIRCULAR    BRICK    SEWERS    PER    LINEAL    FOOT. 


One  Ring. 

Two  Rings. 

Three  Rings. 

Interior  Diameter,  Feet. 

2 

3 

3 

4 

1.71 

.2Q 
-05 

•37 
.58 
q.oo 

5 

2.  IO 
•36 
.07 

•45 
.70 
q.68 

5 

3-36 
•58 
.  II 
.72 
1.  08 

5.8s 

6 

Brick   @,  $8  per  M   . 

.40 
•075 
.015 
.10 

.15 

.74 

.58 
.  II 
.02 
.14 
.22 
1.07 

I-3I 
•23 
.04 
•30 
•  45 
2.33 

3-95 
.70 

•13 

•9* 

1-43 
7.  IT 

Mixed  j  Cement,  @  80  cts.  per  bbl.  . 
i  '  2    )  Sand    @.  50  cts    per  yd 

Masons   (3^  $2  50  

Helpers  @,  $i  50.  .        

Total  .  . 

The  approximate  cost  of  manholes,  3  feet  by  4  feet  6 
inches  on  the  bottom,  is  given  in  the  following  table.  A 
4-foot  circular  manhole  will  cost  about  4  per  cent  more.  This 
table  does  not  include  the  cost  of  the  iron-work.  The  brick- 
work is  taken  as  8  inches  thick  down  to  a  depth  of  12  feet, 
and  below  this  as  12  inches  thick. 

TABLE  No.  24. 

COST  OF    MANHOLES,  3  FT.   X    4  FT.    6    IN. 
(Brick  2  in.  X  4  in.  X  8  in.;  i-inch  joints.) 


Depth,  top  of  Brick-work  to  sewer-invert. 

8ft. 

10  ft. 

12  ft. 

i4  ft. 

i6ft. 

i8ft. 

20  ft. 

Brick    @  $8  per  M      

TO     ?ft 

12    70 

I  ^    Od 

IO    OO 

2-2    2^ 

26    7C. 

•30      jr 

Mixed  \  Cement,  @  80  cts.  per  bbl... 
i  :  2    /  Sand,  @  50  cts.  per  yd  

>  CO  O  C 

">  rr  N  C 

1-4  c 

1.82 

•33 
2    25 

2.15 

.38 

2    GO 

2.72 

.49 

q    CQ 

3-32 
.58 
4   4^ 

3.82 

.68 

e    jc 

4-31 

•75 

57e 

Helpers  @,  $1.50  

2.4O 

2  .70 

o  48 

4-2O 

C  .  <2C 

c.  .  en 

6  oo 

Total  

16.  so 

10.80 

2S  -Q^ 

2Q.QI 

36.  QS 

41  .QO 

46  .  06 

Foundations  of  concrete  6  inches  thick,  with  benches  for  8-inch  pipe  $3.25 

Cast-iron  tops  and  covers,  450  to  800  Ibs.,  @  i£  to  2  cts $5.6o-$i6.oo 

Steps,  wrought-iron,  each 20  cts. 

In  the  above  tables  labor  is  taken  at  $1.50  per  day,  teams 
at  $3.50.  The  cost  given  does  not  include  superintendence, 
use  of  tools,  profit,  or  any  of  the  general  expenses  of  manage- 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.     23! 

ment,  but  is  thought  to  be  liberal,  and  sufficient  to  include 
these  under  good  management. 

Natural  CEMENT  can  be  had  in  the  Eastern  States  at  from 
65  cents  up,  Portland  from  $1.80  up,  per  barrel  in  car-load  lots. 

The  cost  of  SAND  will  vary  with  the  locality  from  25  cents 
to  $2  per  cubic  yard. 


ART.  58.     METHODS  OF  ASSESSMENT. 

While  not  an  engineering  feature  of  sewer  construction, 
the  methods  employed  in  paying  for  a  system  may  be  briefly 
considered  to  advantage.  In  many  cases  the  city  pays  for 
the  construction  and  later  reimburses  itself  by  special  assess- 
ments on  benefited  property  or  by  annual  rental;  in  some 
the  entire  cost  is  borne  by  the  city  at  large;  in  others  part  is 
borne  by  the  city,  part  by  the  property-owners.  The  city's 
payment  may  be  made  from  the  ordinary  funds  or  by  issuing 
sewerage  bonds.  In  Philadelphia,  Pa.,  the  assessment  bills 
are  assigned  to  the  contractor,  with  right  of  lien  for  collection. 

Probably  no  better  general  statement  of  sewer-assessment 
methods  in  this  country  could  be  given  than  by  quoting  from 
an  article  on  the  "  Theory  and  Practice  of  Special  Assess- 
ments," by  J.  L.  Van  Ornum  in  volume  xxxvill  of  the 
Transactions  of  the  American  Society  of  Civil  Engineers 
(September,  1897): 

"  In  a  majority  df  cases  the  city  pays  for  main  sewers, 
either  wholly  or  all  above  the  usual  assessment  for  a  branch 
sewer.  A  large  number  also  assess  this  expense  by  the  area 
method  upon  the  property  affected,  either  entirely  or  all 
exceeding  the  usual  charge  for  a  lateral,  as  before.  Less 
commonly  a  percentage  is  assessed  and  the  city  pays  the 
balance,  or  the  cost  is  divided  between  an  area  and  a  frontage 
charge,  or  other  plans  are  followed  in  its  distribution.  Of  the 


SEWERAGE. 

methods  pursued  in  providing  for  the  collecting  system,  con- 
sisting of  the  laterals  or  branch  sewers,  a  plurality  prefer  to 
charge  the  cost  upon  abutting  property  according  to  the 
frontage  rule;  though  nearly  an  equal  -number  have  an  arbi- 
trary rate  per  foot  front,  varying  from  30  cents  to  $2,  the  city 
to  pay  the  balance;  and  a  considerable  number  assess  the  cost 
either  upon  the  drainage-district  or  upon  a  zone  of  a  certain 
width  on  each  side  of  the  sewer,  in  the  ratio  that  the  area  of 
the  lot  or  land  in  question  bears  to  the  total  assessed  area, 
streets  being  excluded.  Of  the  remaining  methods  some 
divide  the  expense  between  the  city  and  private  property  by 
various  processes,  others  charge  it  upon  property  by  a  com- 
bination of  the  frontage  and  area  rules,  and  sometimes  the 
city  bears  the  whole  cost. 

"  The  frequently  occurring  plan  of  assessing  upon  contigu- 
ous property  the  equivalent  expense  of  a  sewer  of  small  size, 
where  a  large  sewer  is  placed,  is  commendable.  This  method 
would  obviously  have  no  advantage  where  the  total  cost  of 
both  mains  and  branches  are  together  distributed  pro  rata 
upon  all  the  property  benefited,  nor  any  application  where 
the  city  pays  entirely  for  its  sewer  system ;  but  where 
adjacent  property  is  charged  with  a  certain  part  or  all  the 
expense  of  the  sewer,  inequality  would  result  if  the  method 
just  indicated,  or  an  equivalent  specified  fixed  charge  not 
depending  on  the  size  of  pipe,  is  not  applied.  Necessarily 
the  larger  sewers  are  laid  on  the  lower  ground,  where,  except 
manufactoi  ies  and  similar  industries,  the  less  valuable  and 
productive  property  occurs.  Here,  also,  are  more  generally 
found  tenements  and  the  habitations  of  laboring  men  who  are 
less  able  to  meet  the  burden,  while  the  commercial  districts, 
and  especially  the  dwellings  of  the  more  prosperous,  are  in 
the  higher  portions  of  the  city,  where  the  sewers  are  naturally 
of  smaller  size.  The  latter  classes  of  citizens  make  the  greater 
use  of  sewers,  and  it  would  manifestly  be  unjust  to  fail  not 


SPECIFICATIONS,   CONTRACT,  ESTIMATE   OF  COST.     233 

only  to  lay  upon  them  an  equal  burden,  but  to  charge  them 
even  a  smaller  amount  than  the  average.  The  cost  of  appur- 
tenances, like  manholes,  lamp-holes,  catch-basins,  and  flush- 
ing-tanks, is  sometimes  met  by  the  city  and  sometimes 
included  in  the  cost  of  the  sewer  and  so  distributed.  The 
disposition  of  these  expenses  depends  upon  the  provisions  of 
law.  House-connections  with  the  sewer  are  made  at  the 
expense  of  the  property.  In  addition  a  few  cities  impose  a 
special  charge  for  the  privilege  of  connection  for  the  purpose 
of  increasing  the  sewerage  fund  of  the  city,  but  this  is  to  be 
deprecated  as  tending  to  discourage  the  general  use  of  the 
sewers,  which  has  become  a  sanitary  necessity  in  cities. 

"  The  question  of  the  distribution  of  the  cost  of  a  sewer 
system  is  also  a  complicated  one,  whether  considered  in  the 
light  of  practice  or  principle.  All  the  city  has  an  interest, 
both  general  and  sanitary,  in  its  sewers,  and  the  property- 
owners  have  a  direct  interest  as  abutters  as  well  as  a  particu- 
lar, but  more  general,  one  in  the  larger'mains  of  their  district 
sewers.  As  far  as  the  trunk  sewers  are  concerned,  their  con- 
struction is  of  more  general  import  to  the  city  as  a  whole  than 
to  any  individual  users,  and  their  cost  might  well  be  paid  by 
general  taxation.  Whether  or  not  the  city's  share  in  building 
sewers  should  always  be  devoted  to  these  mains,  because  they 
have  the  least  direct  connection  with  property,  may  be 
uncertain,  as  custom  or  local  usage  may  dictate  the  assump- 
tion of  the  cost  of  work  on  street  intersections  or  in  front  of 
city  lots,  parks,  and  other  property,  or  other  expenses, 
besides  the  occasional  defaults  that  come  upon  the  city,  all  of 
which  would  probably  equal  the  proportion  suggested.  All 
the  reasons  already  given  for  considering  it  equitable  for  the 
city  to  share  in  the  expense  of  its  water-works  system  apply 
equally  to  its  sewer  system ;  where  there  are  no  storm-water 
sewers  (a  separate  system)  for  which  the  city  usually  pays,  it 
is  but  just  that  the  city  should  aid  in  the  construction  of  the 


234  SEWERAGE. 

more  usual  combined  system,  which  has  to  receive  the  storm- 
water  from  the  streets.  It  would  be  unfair  to  expect  lots  or 
lands  so  distant  that  they  may  not  be  able  for  years  to  secure 
connection  with  the  system  as  it  develops  to  contribute  much 
toward  paying  for  trunk  sewers  which  will  at  best  be  of  only 
indirect  special  advantage  to  them ;  and  it  is  believed  that  the 
city  assuming  a  share,  to  the  extent  of  20  or  30  per  cent  of 
the  cost  of  its  sewer  system,  would  furnish  but  a  fair  equiva- 
lent for  its  benefit,  and  make  less  burdensome  the  individual 
assessments  which  so  frequently  cause  objection  and  retard 
the  construction  of  these  necessary  improvements. 

"  Of  the  methods  followed  perhaps  the  most  adequate 
plan  of  dealing  with  the  portion  of  the  expense  of  sewers  that 
is  to  be  assessed  is  that  common  one  of  considering  together 
all  the  sewers  of  each  sewer  district  and  distributing  the  cost 
over  the  district  in  proportion  to  the  advantage  received.  In 
many  cities  this  allotment  is  attempted  by  the  frontage  rule,, 
but  deep  lots  generally  have  a  larger  share  in  the  use  of 
sewers  than  have  shallow  ones  of  the  same  frontage.  The 
amount  of  storm-water  to  be  removed  from  lots  is  far  from 
having  a  definite  relation  to  frontage,  and  other  irregularities 
result.  Other  cities  apportion  this  assessment  by  the  area 
rule,  but  of  equal  areas  that  which  has  the  greater  frontage 
enjoys  conditions  favoring  a  larger  number  of  buildings  or 
other  improvements  which  imply  a  greater  interest  in  the 
sewer  system,  and  therefore  should  furnish  a  correspondingly 
larger  contribution;  and  as  systems  are  often  built  a  portion 
at  a  time,  lands  remote  from  the  constructed  portions  should 
not  be  required  to  pay  equally  with  lots  that  are  enabled  to 
make  use  of  them  at  once. 

"  In  consequence  of  the  inequitable  features  inhering  in 
both  systems,  in  numerous  instances  it  has  become  an  im- 
proved method  to  combine  the  two  processes  and  assess  40  per 
cent,  more  or  less,  by  frontage  and  the  balance  by  the  area 


SPECIFICATIONS,   CONTRACT,  ESTIMATE    OF   COST.     2$$ 

rule,  or  to  apply  some  equivalent  procedure  that  will  effect  a 
similar  combination  of  methods.  This  system  of  apportion- 
ment is  growing  in  favor.  It  corrects  the  more  serious  errors 
of  either  method  used  alone.  It  is  not  complex  in  applica- 
tion, and  in  principle  it  is  as  definite  and  as  easily  understood 
by  the  people  affected  as  either  single  process.  Probably  no 
more  adequate  plan  for  sewer  assessments  has  been  exten- 
sively used  than,  after  the  city  has  contributed  its  due  por- 
tion, assessing  by  frontage  an  amount  equal  to  the  cost  of  a 
smaller  size  of  pipe  upon  abutting  property,  as  previously 
mentioned,  or  an  equivalent  amount,  and  distributing  the 
remainder  in  proportion  to  area. 

"  In  some  Massachusetts  cities  the  plan  has  recently  been 
applied  of  partly  paying  the  cost  of  the  sewer  system  and  its 
maintenance  by  a  sewer  rental  corresponding  in  its  principle 
to  the  water  rates  of  water-works  systems.  The  private  con- 
tribution to  sewerage  construction  should  correspond  very 
closely  to  the  use  made  of  them ;  and  to  effect  this  Brockton 
and  other  Massachusetts  towns  have  adopted  the  plan  of  such 
an  annual  charge  depending  upon  the  amount  of  water  used, 
claiming  that  the  quantity  of  sewage  to  be  disposed  of  can  be 
approximately  estimated  by  reference  to  the  water  rate.  If 
this  plan  does  not  tend  to  discourage  the  use  of  sewers,  if  it 
does  not  too  much  complicate  the  system  of  assessment  and 
proves  otherwise  practicable,  it  may  furnish  a  valuable  addi- 
tion to  the  methods  of  apportionment.  Its  practical  opera- 
tion will  be  watched  with  interest  by  those  making  a  study  of 
special  assessments." 

Since  the  assessment  is  strictly  a  legal  function,  the  State 
laws  and  city  charter  will  to  some  extent  control  the  methods 
in  each  particular  case.  For  instance,  in  New  Jersey  assess- 
ment by  the  front  foot  has  been  decided  illegal.  It  is  prob- 
able that  in  all  States  it  is  legal  to  assess  in  proportion  to 
benefits  received,  and  this  too  would  seem  to  be  demanded 


236  SEWERAGE. 

by  fairness.  These  benefits  consist  of:  (i)  removal  of  house- 
sewage  from  the  buildings;  (2)  removal  of  rain-water  from 
premises  and  streets  (where  combined  or  storm  sewers  are 
built);  (3)  draining  the  land  when  wet;  (4)  increasing  the 
value  of  property;  (5)  a  general  public  benefit  to  the  entire 
city,  whether  it  is  all  sewered  or  not,  consequent  on  the  im- 
proved healthfulness  of  certain  sections,  on  increased  valua- 
tion and  therefore  reduced  tax  rates,  and  on  the  recommen- 
dation to  prospective  residents  that  it  "  has  sewers."  The 
1st,  3d,  and  4th  are  individual  benefits,  the  2d  a  combination 
of  individual  and  general,  the  $th  a  general  one.  It  would 
appear,  therefore,  that  a  perfectly  just  apportionment  of  the 
cost  would  assess  part,  but  only  a  part,  of  this  upon  property 
directly  benefited,  and  this  at  fixed  rates  in  proportion  to 
front  foot  and  area  combined,  with  an  additional  charge  for 
each  connection  made  or  an  annual  rental  in  lieu  thereof. 
This  charge  may  be  collected  either  as  an  assessment,  to  be 
paid  at  once  or  to  bear  interest  and  be  apportioned  into  sev- 
eral annual  payments ;  or  in  the  form  of  rentals,  at  fixed  rates 
for  the  different  classes  of  sewage-contributors  or  else  propor- 
tioned to  some  function  of  the  water-consumption.  The 
method  employed  at  Maiden,  Mass.,  of  giving  each  property- 
holder  the  option  of  either  of  these  methods  has  some  advan- 
tages. It  is  in  most  cases  desirable  to  make  each  assessment 
or  rental  operative  as  soon  as  it  becomes  possible  to  connect 
the  property  with  the  sewer  and  make  use  thereof,  as  tend- 
ing to  hasten  the  general  use  of  the  system.  Whatever  the 
method  it  should  be  simple  of  application  and  readily  under- 
stood, should  not  be  burdensome  to  the  poorer  property- 
holders,  and  should  encourage  early  and  general  use  of  the 
sewers. 

For  descriptions  of  various  methods  employed  see  the 
paper  quoted  from  above,  Report  of  the  Engineer  to  the 
Brockton  Sewerage  Commission,  and  Journal  of  the  Associa- 
tion of  Engineering  Societies  for  January  and  March,  1897.. 


PART  II. 

CONSTRUCTION. 


CHAPTER   X. 
PREPARING   FOR  CONSTRUCTION.  , 

ART.  59.     CONTRACT  WORK  OR  DAY  LABOR. 

THERE  are  two  general  plans  by  which  a  city  or  town  may 
construct  a  sewerage  system,  viz.,  by  contract  or  by  day 
labor.  In  a  majority  of  instances,  probably  a  very  large  one, 
the  contract  method  is  adopted,  but  in  quite  a  number  the 
work  is  done  under  the  general  charge  of  the  city  engineer  or 
a  special  agent  or  committee  who  purchases  material,  employs 
labor,  and  looks  after  the  work  generally.  If  the  work  can  be 
kept  entirely  free  from  politics  and  conducted  without  "  fear 
or  favor  "  by  a  good  manager  experienced  in  this  line  of  work 
the  latter  method  will  probably  be  the  more  economical  for 
the  city  and  give  the  more  satisfactory  results.  Unfortu- 
nately these  conditions  exist  in  few  cities  or  towns,  and  the 
contract  method  is  usually  the  cheaper  one,  and  frequently 
gives  better  results  than  construction  by  home  labor  under 
foremen  too  often  unskilled  in  sewerage-work.  There  may 
be  cases  where,  even  with  and  in  spite  of  the  existence  of  the 
above  objections,  construction  directly  by  the  city  is  prefer- 
able. For  instance,  the  work  may  be  of  an  uncertain  nature, 

237 


238  SEWERAGE. 

its  details  difficult  to  foresee  and  set  forth  in  a  contract;  or  it 
may  be  unusually  hazardous,  causing  contractors  to  add  100 
or  even  200  per  cent  to  the  estimated  cost  to  balance  the  risk, 
which  risk  the  city  might  think  it  better  to  assume  itself.  In 
some  instances  villages  have  undertaken  sewerage-work  as  a 
means  of  giving  employment  in  unusually  hard  times  to 
citizens,  who  would  thus  be  enabled  to  pay  part  of  their  wages 
back  to  the  treasury  in  taxes,  and  also  relieve  the  poorhouse 
of  a  large  number  of  possible  inmates. 

Since,  however,  sewerage-work  is  generally  done  by  con- 
tract, the  succeeding  chapters  will  be  made  applicable  particu- 
larly to  construction  by  this  method.  But  the  matter  is 
equally  applicable  to  work  done  by  the  city  or  its  immediate 
agent,  which  agent  should  conduct  the  work  as  the  contractor 
would  have  been  compelled  to  conduct  it. 

It  may  be  sometimes  advisable  for  the  city  to  purchase 
the  materials  and  contract  for  the  labor  of  construction.  In 
this  way  the  quality  of  the  materials  is  under  the  immediate 
control  of  the  city.  In  the  matter  of  cost  there  is  usually 
very  little  difference  one  way  or  the  other,  unless  it  be  that 
the  city  is  charged  a  little  more,  owing  to  a  "  commission  " 
which  must  be  paid  to  certain  officials  who  control  the  award- 
ing of  the  contracts  for  material.  It  is  an  excellent  plan  for 
the  city  to  furnish  cement,  sand,  and  pipe,  and  see  that  there 
is  no  unnecessary  waste  of  these.  There  is  then  no  tempta- 
tion for  the  contractor  to  use  defective  material  or  too  little 
cement. 

Systems  have  been  built  by  letting  the  contract  for  exca- 
vation to  one  party,  and  that  for  pipe-laying  and  brick-work 
to  others,  the  material  being  purchased  by  the  city.  This  is 
almost  sure  to  work  unfavorably  to  the  city  and  give  rise  to 
the  greatest  confusion,  of  responsibilities  if  not  of  work. 


PREPARING   FOR    CONSTRUCTION. 


ART.  60.     OBTAINING  BIDS. 

If  work  is  to  be  let  by  contract  the  probabilities  are  that 
the  greater  the  number  of  bidders  the  lower  will  be  the  sum 
for  which  the  work  can  be  constructed,  a  partial  cause  of  this 
being  the  lessened  liability  of  collusion  between  the  bidders. 
To  reach  contractors  two  methods  are  open:  to  send  notice  to 
individual  contractors,  or  to  advertise  in  such  a  way  and  place 
as  will  attract  the  attention  of  a  large  number.  Each  method 
has  its  advantages,  and  perhaps  a  combination  of  the  two 
might  give  the  best  results.  But  it  is  probable  that  one  or 
two  advertisements  judiciously  placed  will  reach  all  who  would 
be  reached  by  the  first  method,  and  many  others  besides. 
For  a  small  village  the  best  advertising  medium  is  the  con- 
tractors' journal  having  the  widest  circulation  in  that  part  of 
the  country,  which  is  also  true  for  a  city  if  the  work  amounts 
to  more  than  a  very  few  thousand  dollars.  For  small  con- 
tracts in  cities  having  several  capable  contractors  among  its 
citizens  the  local  paper  will  perhaps  give  sufficient  publicity 
to  the  desire  for  bids,  but  village  papers  are  generally  useless 
for  this  purpose.  For  contracts  of  $5000  or  more  an  adver- 
tisement in  one  or  two  prominent  engineering  and  contracting 
papers  will  usually  pay  for  itself  many  times  over. 

The  customary  method  of  bidding  is  to  have  each  con- 
tractor submit  a  sealed  proposition,  all  of  these  being  opened 
at  a  time  fixed  beforehand.  It  would  be  unfair,  if  not  illegal, 
to  open  any  sealed  bid  before  this  time  or  to  receive  another 
bid  after  any  had  been  opened.  To  satisfy  both  the  public 
and  the  contractors  of  the  honesty  and  fairness  of  the  award- 
ing of  the  contract  it  is  customary  to  open  the  bids  and  read 
them  aloud  at  a  meeting  open  to  the  public,  or  at  least  to  all 
bidders  and  to  newspaper  representatives.  The  opportunities 
for  dishonesty  are  so  great  if  the  bids  are  opened  in  secret  or 


240  SEWERAGE. 

one  received  after  others  have  been  read  that  regard  for  their 
own  reputations  usually  influences  the  officials  making  the 
award  to  adopt  the  above  methods. 

That  there  may  be  no  informal  or  incomplete  bids  it  is 
desirable  that  all  bids  be  made  on  forms  furnished  by  the  city 
and  accompanied  by  copies  of  the  specifications  and  contract 
similarly  furnished.  It  would  be  possible  for  a  bidder  whose 
bid  had  been  accepted  to  refuse  to  contract  for  the  work 
unless  he  were  bound  in  some  way.  For  this  reason  it  is  well 
to  require  that  each  bid  be  accompanied  by  a  certified  check, 
to  be  returned  to  the  bidder  unless  he  refuse  to  sign  the  con- 
tract based  upon  his  bid,  if  so  requested. 

The  laws  of  different  States  and  cities  differ  as  to  the  lati- 
tude given  in  awarding  contracts.  In  some  the  contract  must 
be  awarded  to  the  "  lowest  bidder,"  in  others  to  the  "  lowest 
responsible  bidder,"  while  in  still  others  there  is  no  restric- 
tion. Justice  to  the  taxpayers  and  fairness  to  the  bidders 
will  usually  dictate  awarding  to  the  lowest  bidder,  unless 
there  be  reason  to  think  that  he  will  be  unable,  through 
inexperience,  to  do  creditable  work,  or  that,  his  bid  being 
lower  than  the  work  can  probably  be  done  for,  he  will  later 
abandon  the  work,  and  the  consequent  delay  and  legal  com- 
plications, even  though  his  bond  insure  the  ultimate  comple- 
tion of  the  contract,  will  be  detrimental  to  the  city's  interests., 
If  it  becomes  evident  during  construction  that  the  contractor 
cannot  but  lose  money  there  is  usually  a  tendency  to  favor 
him  in  minor  matters,  to  grant  him  extensions  of  time  and 
aid  him  in  other  ways  which  detract  more  or  less  from  the 
excellence  of  the  work.  In  order  to  avoid,  on  the  other  hand, 
the  necessity  of  awarding  the  contract  to  a  too  high  bidder 
when  there  are  no  reasonably  low  ones  the  city  should 
"  reserve  the  right  to  reject  any  or  all  bids." 


PREPARING   FOR    CONSTRUCTION.  24! 


ART.  61.     ENGINEERING  WORK  PRELIMINARY  TO 
CONSTRUCTION. 

As  soon  as  possible  after  the  signing  of  the  contract  the 
contractor  should  submit  samples  of  the  material  he  wishes 
to  use,  and  these  should  be  carefully  examined  by  the 
engineer,  and  if  accepted  should  be  retained  and  marked  for 
future  identification  and  compared  from  time  to  time  with 
the  material  actually  furnished. 

The  contractor  should  be  notified  some  days  in  advance 
of  the  point  or  points  at  which  he  is  to  begin  work.  Reason- 
able deference  should  be  made  to  his  wishes  in  this  matter, 
since  it  is  his  privilege  and  duty  to  so  organize  the  work  as  to 
secure  the  greatest  efficiency  at  the  least  cost  to  himself.  If, 
for  instance,  part  of  the  work  lies  through  wet  ground  and 
sub-drains  are  to  be  used  it  is  ordinarily  to  his  interest,  and 
indirectly  to  the  city's  also,  that  the  work  begin  at  an  outlet 
to  which  all  ground-water  will  drain,  or  at  a  point  at  which  a 
pump,  once  set  up,  can  drain  the  work  for  long  distances 
without  moving  its  location,  as  at  the  junction  of  two  mains. 
It  is  also  usually  desired  by  the  contractor  that,  if  two  or 
three  gangs  are  to  work  at  as  many  places,  they  may  be 
within  a  few  blocks  of  each  other  for  convenience  of  oversight. 
It  will  ordinarily  be  to  the  interests  of  both  contractor  and 
city  to  work  in  as  dry  ground  as  possible,  and  hence  to  leave 
until  summer  droughts  construction  through  low,  soggy  land. 
Construction  across  or  near  streams  should  not  be  carried  on 
when  there  is  a  possibility  of  floods  or  freshets,  if  it  can  be 
avoided.  Both  trench-  and  masonry-work  should  be  avoided 
in  winter  weather  if  possible,  for  it  is  then  costly  to  the  con- 
tractor, and  it  is  impossible  to  be  sure  that  the  mortar  is 
uninjured,  or  to  restore  the  streets  to  good  condition  with 
frozen  earth. 


242  SEWERAGE. 

Ordinarily  the  contractor  will  desire  to  place  upon  the 
street,  along  the  line  of  the  work,  pipe,  brick,  sand,  lumber, 
etc.,  This  cannot  be  denied  him,  but  he  should  be  compelled 
to  place  and  pile  this  material  so  as  to  interfere  with  travel  as 
little  as  possible,  and  along  only  those  stretches  of  street  in 
which  construction  is  to  be  begun  within  a  week,  or  ten  days 
at  the  outside.  This  material  should  be  inspected  as  it  is 
delivered,  and  that  condemned  removed  at  once. 

Just  before  the  work  begins  it  is  well  to  run  levels  care- 
fully over  all  bench-marks  to  see  that  they  have  not  been 
disturbed  and  to  check  previous  levelling;  also  to  establish 
new  ones  if  necessary.  It  is  desirable  to  so  place  these  that 
one  of  them  can  be  seen  from  the  instrument  when  set  up  for 
giving  grades  to  any  part  of  the  work.  They  should  be 
accurate  within  at  least  .003  of  a  foot. 

ART.  62.     OTHER  PRELIMINARIES. 

Final  arrangements  should  now  be  made  for  the  oversight 
of  the  work,  the  proper  instruments  obtained,  engineering  and 
inspecting  assistants  engaged,  an  office  or  other  headquarters 
arranged  for,  notebooks  and  blanks  obtained  for  making  and 
preserving  records,  final  arrangements  made  as  to  right  of  way 
across  private  property  and  along  county  roads  or  others  not 
controlled  by  the  city  or  village.  Arrangements  should  be 
made  also  for  locating  the  branches  for  house-connections  at 
the  points  desired  by  the  property-owners.  For  this  purpose 
it  is  well  to  publish  in  the  paper  or  otherwise  make  known  to 
the  citizens  that  each  is  desired  to  drive,  at  his  fence-line  or 
curb,  a  stake  indicating  the  point  at  which  he  wishes  his 
house-connection  to  enter  his  property,  and  that  in  case  no 
such  stake  is  driven  the  engineer  or  inspector  will  use  his 
judgment  in  locating  such  branches.  Another  method  is  that 
of  requesting  that  sketches  of  the  property  showing  such 


PREPARING   FOR    CONSTRUCTION.  243 

point  be  handed  in  on  blanks  to  be  furnished  by  the  engineer; 
but  the  inability  or  hesitancy  of  many  citizens  to  make  the 
simplest  drawing  is  an  objection  to  this  plan. 

Counsel  for  the  city  should  pass  upon  the  sufficiency  and 
correctness  of  the  contracts  signed,  of  the  bonds  given  and  of 
their  signers,  and  all  other  legal  matters  in  connection  there- 
with, before  the  contractor  is  permitted  to  begin  work. 


CHAPTER   XI. 
LAYING   OUT   THE   WORK. 

ART.  63.     LINING  OUT  TRENCHES. 

SINCE  the  trench  is  seldom  more  than  6  inches  wider  on 
each  side  at  the  bottom  than  the  sewer  to  be  placed  in  it,  it 
is  necessary  that  the  trench  itself  be  carefully  aligned,  and 
this  cannot  be  entrusted  to  the  contractor  except  for  short 
distances.  For  giving  him  the  line  the  safest  plan  is  to  drive 
stakes  or  spikes  along  the  centre  of  the  proposed  trench  at 
intervals  of  about  50  feet.  To  assist  in  finding  these,  for 
checking,  and  to  locate  the  centre  of  the  sewer  during  con- 
struction, the  distance  should  be  taken  from  each  of  these  to 
the  curbing  opposite,  if  there  is  any,  or  to  a  reference-stake, 
and  a  note  made  of  this.  The  centre  spikes  or  stakes  should 
be  some  uniform  distance  apart  to  facilitate  finding  them. 
They  should  be  set  by  a  transit  placed  over  the  centre  of  a 
manhole  on  the  line.  The  line  should  of  course  be  straight 
between  manholes,  except  in  the  case  of  large  sewers,  which 
may  be  curved,  in  which  case  the  centre  stakes  should  be  set 
10  or  15  feet  apart.  The  location  of  manholes,  flush-tanks, 
etc.,  should  be  fixed  by  two  or  more  reference-stakes  and 
pointed  out  to  the  contractor  before  he  begins  excavating, 
that  he  may  make  allowance  for  them  in  sheathing. 

Some  engineers  in  giving  line  rely  entirely  upon  reference- 
stakes  placed  a  uniform  distance  from  the  centre  of  the  trench,. 

244 


LAYING    OUT   THE    WORK.  24$ 

because  the  centre  stakes  will  be  removed  in  excavating.  An 
experience  with  the  unreliability  of  contractors'  tapes  and 
foremen's  intelligence  seems  to  argue  in  favor  of  the  centre 
stakes,  however. 

It  is  well  to  do  a  large  part  of  this  lining  out  before  con- 
struction gets  well  under  way,  since  it  is  probable  that  the 
engineer  corps  will  be  kept  busy  with  other  work  later.  Each 
line  should  be  located  only  after  due  consideration  of  the 
points  referred  to  in  Art.  34. 


ART.  64.     GIVING  GRADE. 

Several  methods  of  giving  grade  are  employed  by  different 
engineers,  the  principal  being:  By  means  of  a  cord  stretched 
over  the  centre  of  the  trench  and  parallel  to  the  sewer  grade ; 
by  stakes  driven  to  grade  along  the  centre  line  in  the  bottom 
of  the  trench;  and  by  stakes  driven  at  the  ground-surface  near 
the  edge  of  the  trench,  their  tops  a  uniform  or  stated  distance 
above  the  sewer  grade.  (The  grade  used  in  both  designing 
and  construction  is  that  of  the  inside  bottom  of  the  invert, 
which  for  convenience  will  be  called  the  invert.)  Each  of 
these  is  used  for  both  pipe  and  brick  sewers,  but  only  the  first 
method  is  at  all  adapted  to  accurate  laying  of  pipe  sewers. 
For  brick  sewers  either  method  may  be  used,  but  the  first  is 
most  convenient  in  that  the  invert-templet  can  be  set  at  any 
point  along  the  trench,  and  that  the  bottom  of  the  trench  can 
be  carried  to  the  exact  grade  at  every  point,  in  advance  of 
setting  the  templet,  by  measuring  down  from  the  cord.  If 
stakes  are  driven  in  the  bottom  the  templets  can  be  accurately 
set  only  at  points  close  to  these,  and  the  stakes  can  be  driven 
only  when  the  bottom  is  within  a  foot  or  less  of  grade,  which 
necessitates  the  presence  of  the  engineer  upon  the  work 
almost  constantly.  If  the  stakes  are  driven  along  the  edge  of 


246 


SEWERAGE. 


the  trench  they  can  be  set  even  before  the  excavation  has 
been  begun,  enough  for  several  days  in  advance  being  set  at 
one  time;  but  it  is  almost  impossible  to  avoid  errors  in 
measuring  down  from  these,  since  they  are  not  directly  above 
the  sewer,  and  the  stakes  are  apt  to  become  loose  or  fall  out 
with  the  cracking  and  caving  of  the  edge  of  the  trench. 

The  cord  used  in  the  first  method  may  be  fastened  to  a 
strip  of  wood  nailed  in  a  vertical  position  to  a  plank  which 
stands  upon  edge  with  one  end  resting  upon  the  ground  on 
each  side  of  the  trench.  This  plank  should  extend  at  least  18 
inches  or  2  feet  beyond  the  trench  on  each  side  and  be  firmly 
bedded  into  solid  ground  so  that  it  cannot  possibly  settle,  and 
should  be  held  upright  on  edge  by  a  stake  driven  on  each  side 
at  each  end,  or  by  stones  and  earth  solidly  banked  around  the 
ends.  These  grade-planks  should  be  not  more  than  33^  feet 


FIG.  5. — METHOD  OF  SETTING  GRADE-PLANK. 

apart — 25  feet  would  perhaps  be  better,  since  the  cord  will  sag 
too  much  if  the  distance  between  supports  be  greater.  On 
the  top  edge  of  these  planks  the  centre  of  the  trench  is 
marked,  and  strips  of  wood  about  I  inch  X  2  inches  X  24 
inches  are  nailed  so  that  one  edge  of  each  is  in  this  centre  line 
and  truly  vertical,  as  determined  by  a  plumb-bob.  On  this 
edge  is  placed  a  mark  exactly  a  whole  number  of  feet  above 
the  sewer-invert  immediately  beneath,  and  a  slight  notch  is 
cut  to  receive  the  cord.  All  notches  in  a  given  length  of 


LAYING    OUT    THE    WORK. 


247 


sewer  are  placed  the  same  distance  above  the  sewer-invert, 
and  the  cord  stretched  from  one  to  the  other  is  therefore 
parallel  to  the  grade,  which  can  be  found  at  any  point  by 
measuring  the  given  fixed  distance  down  from  the  cord.  The 
cord  is  also  vertically  above  the  centre  line  of  the  sewer.  If 
the  trench  changes  in  depth  or  for  some  reason  it  is  desirable 
to  change  the  distance  from  the  cord  to  the  sewer-invert,  a 
step  up  or  down  must  be  made  at  some  grade-plank  by  cutting 
two  notches  one  or  two  feet  apart  in  elevation.  The  cord 
should  be  strong  linen  fish-line  or  similar  material  whose  light 
weight  will  prevent  unnecessary  sagging,  and  should  be 
stretched  tightly  between  the  grade-planks. 

Another  method  of  supporting  the  string  is  to  drive  at 
equal  intervals  stout  stakes,  at  least  2  inches  X  4  inches  X  5 


FIG.  6. — METHOD  OF  SETTING  GRADE-PLANK. 

feet  in  dimension,  on  each  side  of  and  about  3  feet  back  from 
the  trench,  and  in  pairs  directly  opposite  each  other.  On  each 
of  these  is  found  a  point  a  certain  whole  number  of  feet  above 
the  sewer-invert  and  usually  2  or  3  feet  above  the  ground, 
and  a  straight-edged  board  or  plank  is  nailed,  one  end  to  each 
stake,  with  its  upper  edge  exactly  at  these  points.  On  this 
edge  is  marked  the  centre  of  the  trench  and  a  slight  notch 
cut  there  to  receive  the  cord.  One  end  of  the  cord  is  fastened 
to  a  nail  driven  into  the  first  board  below  the  notch,  and  rests 


248 


SEWERAGE. 


in  this  notch  and  those  of  succeeding  boards,  and  is  fastened 
at  its  other  end  to  another  nail  placed  as 
is  the  first.  Or  a  large  spool  is  cut  as 
shown  in  Fig.  7  and  caught  behind  the 
board,  the  cord  being  fastened  in  it  and 
being  readily  tightened  whenever  it  be- 
comes loose.  This  method  of  elevated 

FIG.    7.— METHOD    OF  .  .  . 

HOLDING     GRADE-  grade-boards    is  particularly  applicable  to 

RD*  large  pipe  sewers  or  small  brick  ones,  since, 

the  cord  being  higher  above  the  ground,  it  interferes  less  with 
the  lowering  of  materials  into  the  trench.  In  some  cases  it  is 
not  wise  to  adopt  it  on  account  of  the  liability  of  the  banks  to 
be  caved  in  by  the  driving  of  the  posts. 

In  laying  pipe  sewers  from  the  cord  a  grade-rod  is  used 
with  a  mark  or  notch  on  its  edge  so  placed  that  when  it  is 
level  with  the  string  the  foot  of  the  rod  is  level  with  the 
sewer-invert  or  with  the  outside  top.  The  former  is  prefer- 
able, since  the  invert  is  the  part  of  the  pipe  which  it  is  most 
important  to  have  at  correct  grade,  and,  as  the  pipes  often 
vary  slightly  in  diameter,  this  result  may  not  be  obtained  if 
they  are  graded  by  their  tops.  If  the  inverts  are  to  be  set 
it  will  be  necessary  to  have  an  offset-piece 
at  the  foot  of  the  grade-rod  which  can 
rest  inside  the  pipe  upon  the  invert.  For 
this  purpose  an  ordinary  cast-iron  6-  or 
8-inch  bracket,  obtainable  at  any  hard- 
ware-store, will  answer;  or  wrought  iron 
may  be  used  if  about  J  inch  thick  and 
stiffened  by  being  bent  back  upon  the 
rod.  The  mark  on  the  grade-rod  should 
be  checked  each  day.  FlG-  S.-GRADE-ROD. 

For  brick  sewers  each  templet  is  set  by  a  rod,  and  for  both 
these  and  pipe  sewers  another  rod  is  used  by  the  foreman  for 
getting  the  excavation  to  the  proper  depth. 


LAYING    OUT    THE    WORK.  249 

The  grade-plank  or  stakes  above  described  can  be  set  out 
even  before  excavation  is  begun,  but  except  in  shallow 
trenches  it  is  better  to  wait  until  the  trench  is  at  least  6  feet 
deep,  that  they  may  interfere  with  the  excavating  as  little  as 
possible.  It  is  often  well,  however,  to  drive  the  stakes,  where 
these  are  used,  before  excavating  to  prevent  cracking  the 
bank,  the  board  not  being  nailed  to  them  until  afterward. 
The  grade-plank  and  stakes  should  be  tested  for  grade  and 
line  at  least  once  a  day,  and  the  inspector  should  keep  close 
watch  of  them  to  see  that  they  are  not  disturbed  and  also 
that  the  cord  is  kept  taut. 

When  excavating-machinery  is  used  the  grade-planks 
cannot  ordinarily  be  placed  above  the  surface,  but  they  can 
be  sunk  into  the  ground  entirely  below  the  surface,  or  the 
bracing  of  the  trench  can  be  utilized  by  nailing  the  vertical 
strips  to  it.  This  latter  method  is  also  preferable  for  pipe 
sewers  when  the  trench  is  very  deep,  since,  if  the  cord  is  at 
the  surface,  the  grade-rod  is  too  long  for  convenience  and 
accuracy,  and  the  inspector  is  too  far  from  the  work  of  sewer 
construction  to  watch  properly  both  it  and  the  grade-rod. 

In  trenches  through  running-  or  quicksand  unless  the 
utmost  care  is  taken  the  banks  will  settle  several  inches  or 
even  feet,  carrying  the  grade-plank  with  them  of  course. 
Under  such  circumstances  a  level  should  be  kept  constantly 
on  the  ground  and  the  grades  checked  every  few  minutes 
during  pipe-laying  or  at  the  time  of  setting  templets.  More- 
over, the  bench-marks  themselves,  when  on  curbing,  fire- 
hydrants,  or  elsewhere  near  the  roadway,  may  settle  and 
should  be  checked  daily. 

For  properly  fixing  the  grade  of  a  manhole-head  a  stake 
may  be  driven  near  by  indicating  the  street  grade,  and  it 
would  also  be  well  to  test  the  head  by  the  level  as  it  is  being 
set.  Similar  stakes  should  be  set  for  storm-water  inlets. 


250  SEWERAGE. 

Inlet-  and  house-connections  should  be  laid  as  truly  to  line 
and  grade,  and  in  the  same  way,  as  the  sewer  itself. 

Where  grade-stakes  in  the  bottom  are  used  these  are  set 
to  the  exact  grade  of  the  invert  or  one  foot  above  it.  For 
pipe  sewers  the  bottom  of  the  trench  is  then  given  a  uniform 
grade  from  one  stake  to  another  by  using  a  straight-edge, 
stretching  a  cord,  or  too  often  by  eye  only,  and  the  pipe  is 
laid  on  this  bottom  and  lined  in  by  eye.  Great  accuracy  can 
hardly  be  expected  by  this  method.  For  brick  sewers,  how- 
ever, it  compares  favorably  with  the  cord  for  accuracy  (but 
not  for  convenience),  the  stakes  being  driven  in  the  centre 
line  of  the  sewer  and  at  such  distances  apart  that  each  templet 
can  be  set  close  to  a  stake. 

Stakes  driven  upon  the  bank  are  not  recommended  for  any 
purpose,  it  being  almost  impossible  to  obtain  accurate  results 
by  their  use.  Their  only  advantage  is  that  setting  them 
gives  less  trouble  to  the  engineer  than  either  of  the  other 
methods. 

Alleged  sewers  have  been  laid  with  a  carpenter's  level  2  feet 
long,  to  the  under  side  of  one  end  of  which  was  fixed  a  piece 
of  wood  or  iron  or  a  screw  protruding  an  amount  equal  to  the 
desired  rise  in  that  distance.  It  would  be  an  exceptional  case 
in  which  a  line  of  sewer  so  laid  did  not  vary  more  than  one 
inch  in  each  100  feet  from  the  desired  grade. 

While  giving  grades  the  measurement  of  the  sewer-lines 
should  be  carefully  made  and  noted  and  compared  with  the 
original  measurements,  and  if  any  appreciable  difference  is 
found  the  sewer  grades  upon  the  plans  must  be  readjusted  to 
correspond.  Careful  notes  should  be  kept  of  all  instrumental 
work  connected  with  giving  line  and  grade.  It  will  be  con- 
venient to  have  in  each  level-notebook  a  list  of  all  bench- 
marks in  the  sewer-district  in  which  it  is  to  be  used. 

Both  inspector  and  engineer  should  watch  for  the  first 
indication  of  the  existence  in  the  trench  of  an  obstruction  to 


LAYING    OUT   THE    WORK.  2$  I 

the  sewer,  that  preparation  may  be  made  for  a  change  in  line 
or  grade  if  necessary  to  pass  the  obstruction.  Such  change, 
if  in  line,  may  necessitate  inserting  one  or  two  additional 
manholes  or  a  lamp-hole ;  if  in  grade  it  may  be  made  by  a 
decrease  in  grade  in  one  stretch  and  an  increase  in  the  next, 
or  by  siphoning  under  or  over  the  obstruction  (see  Art.  49), 
In  some  cases  the  change  can  be  made  in  the  obstruction  and 
not  in  the  sewer. 

It  is  the  inspector's  duty  to  see  that  house-  and  inlet-con- 
nection branches  are  inserted  at  the  proper  points,  and  their 
exact  locations  noted,  which  locations  the  engineer  must  make 
note  of  and  reference  to  some  fixed  point,  usually  the  centre 
of  the  nearest  manhole,  to  make  possible  the  ready  finding  of 
the  branches  in  the  future.  This  is  very  important  and  should 
be  faithfully  attended  to. 


CHAPTER   XII. 
OVERSIGHT   AND   MEASUREMENT   OF   WORK. 

ART.  65.     INSPECTION  OF  WORK. 

THE  specifications  are  practically  the  instructions  to  the 
contractor  as  to  the  way  in  which  the  sewerage  system  is  to 
be  built,  the  lines,  grades,  and  dimensions  being  given  by  the 
engineer,  chief  or  assistant.  If  the  contractor  were  left 
unwatched  to  carry  out  these  instructions  it  would  be  impossi- 
ble to  know  whether  he  had  done  so  or  not,  since  only  the 
inside  of  the  sewer  can  be  examined,  and  this  only  with  diffi- 
culty. And  if  it  were  found,  after  the  completion  of  the 
work,  that  it  had  been  improperly  built  or  of  poor  material, 
even  though  the  contractor  could  be  compelled  to  replace  it 
with  satisfactory  work,  the  delay  and  inconvenience  of  this 
might  better  be  avoided  by  proper  oversight  during  construc- 
tion. It  is  advisable,  therefore,  that  a  competent  inspector 
be  constantly  on  hand  when  any  construction  is  progressing. 
This  is  not  necessary  during  excavation,  but  even  this  should 
be  looked  after  at  least  once  a  day,  that  any  unforeseen 
underground  condition  which  may  modify  the  plans  may  be 
noted,  and  in  general  to  ascertain  that  the  contractor  is 
obtaining  the  proper  width  of  trench,  is  not  interfering  un- 
necessarily with  private  drains,  water-  or  gas-pipes,  and  is  in 
general  following  the  directions  for  trenching,  blasting,  etc. 

For  this  oversight  it  will  usually  be  necessary  to  have  an 
inspector  for  each  set  of  pipe-layers  and  of  masons.  But  if 

252 


OVERSIGHT  AND    MEASUREMENT   OF   WORK.         253 

only  one  or  two  trenches  are  being  worked  at  a  time  the 
instrument-man  may  also  be  inspector.  The  omissions  and 
poor  work  which  may  be  accepted  from  the  contractor  if  such 
inspection  is  not  constantly  made  may  be  seen  from  a  state- 
ment of  the  inspector's  duty. 

The  inspector  should  be  on  hand  before  work  is  begun  at 
morning  and  noon  to  see  that  no  mortar  left  from  the  previous 
day  is  worked  over,  that  new  mortar  is  properly  proportioned 
and  mixed,  and  to  examine  grade-lines  or  -stakes.  In  the 
case  of  pipe  sewers  he  should  examine  the  inside  of  the  sewer 
near  the  end  and  see  that  any  stones,  dirt,  or  other  matter 
which  may  be  there  be  removed  before  the  laying  begins. 
He  should  also  examine  the  one  or  two  cemented  joints 
nearest  the  end,  and  if  they  are  not  sound  the  pipe  should  be 
removed  and  relayed.  In  the  case  of  brick  sewers  he  should 
examine  the  toothing  at  the  end  of  the  brick-work  and  have 
removed  any  loose  brick  and  all  mortar  and  dirt  that  may  be 
lodged  there. 

He  should  continually  keep  an  eye  upon  material  and 
workmanship,  examining  each  pipe  before  it  is  lowered  into 
the  trench,  each  load  of  brick  and  of  sand  as  they  are  brought 
upon  the  ground,  each  barrel  or  bag  of  cement  to  see  that  it 
bears  the  engineer's  mark  or  is  of  the  required  make  and  that 
it  is  not  caked  by  moisture.  He  should  see  that  the  proper 
proportions  of  cement  and  sand  are  used  for  the  mortar,  and 
that  no  mortar  partially  set  is  retempered  and  used. 

On  brick  sewers  he  should  see  that  each  templet  used  is 
one  approved  by  the  engineer  and  that  it  is  set  to  the  proper 
grade  and  line,  that  the  brick  are  laid  to  line  and  in  accordance 
with  the  specifications,  that  slants  or  other  branches  are  set 
where  needed,  and  he  should  keep  an  accurate  account  of 
these,  their  size  and  length,  and  mark  the  position  of  each  by 
a  stake  driven  in  the  bank  directly  over  it  for  the  information 
of  the  engineer.  He  should  see  that  the  arch-centre  is  solid 


254  SEWERAGE. 

and  does  not  spring  under  the  brick-work,  and  that  it  is  not 
drawn  too  soon. 

On  pipe  sewers  he  should  see  that  each  pipe  is  laid  to 
grade  and  line  by  the  use  of  the  grade-rod  and  a  plumb-bob 
in  connection  with  the  grade-cord,  that  each  pipe  is  pushed 
*'  home,"  each  joint  properly  cemented  and  the  swab  or  piston 
in  the  sewer  pulled  forward,  and  that  the  back-filling  is 
properly  placed  and  tamped  around  the  pipe.  He  should  see 
that  house-branches  are  placed  where  directed,  that  covers 
are  cemented  in  each  one  (about  this  he  is  sometimes  careless, 
to  the  great  detriment  of  the  sewer),  and  should  drive  a  stake 
in  the  bank  directly  over  each. 

He  should  keep  a  record  of  all  extra  work,  or  work,  such 
as  foundations  or  sheathing  left  in  the  trench,  which  cannot 
be  measured  after  the  completion  of  the  sewer. 

If  the  ground  is  wet  he  should  see  that  no  water  flows 
over  the  brick-work  or  through  the  pipe,  except  as  permitted 
by  the  engineer.  In  general  he  should  be  thoroughly  familiar 
with  the  specifications  and  have  a  copy  constantly  on  the 
work,  and  see  to  their  enforcement,  reporting  to  the  engineer 
any  difficulty  in  obtaining  this. 

He  should  not  be  permitted  to  be  in  any  way  indebted  to, 
or  under  the  influence  and  power  of,  the  contractor,  and 
should  receive  orders  from  the  engineer  only. 

He  should  be  a  man  with  some  experience  in  the  character 
of  work  he  is  inspecting,  sober,  and  having  the  respect  of  the 
contractor  and  workmen. 


ART.  66.     DUTIES  OF  THE  ENGINEER. 

The  engineer  should  keep  constantly  in  touch  with  the 
work,  visiting  each  point  at  least  once  a  day,  and  giving 
necessary  instructions  to  the  contractor  and  inspector,  as  well 
as  giving  and  testing  line  and  grade.  If  he  has  many 


OVERSIGHT  AND    MEASUREMENT   OF   WORK.         2$$ 

inspectors  on  work  under  his  charge  they  should  be  required 
to  report  at  the  engineer's  office  after  each  day's  work  the 
amount  done  and  return  a  detailed  statement  of  any  extra 
work,  asking  instructions  on  any  points  concerning  which  they 
are  in  doubt.  The  daily  reports  may  be  made  in  writing  upon 
blanks  furnished  to  the  inspectors  for  this  purpose. 

The  engineer  must  see  that  each  inspector  is  performing 
his  duty,  and  if  necessary  enforce  instructions  given  by  him 
to  the  contractor.  He  must  inspect  all  material  to  be  used, 
where  this  is  possible,  or  give  the  inspector  full  instructions 
on  this  point  where  it  is  not.  It  is  well  to  mark  each  accepted 
barrel  or  bag  of  cement;  to  inspect  the  pipe  after  it  is  deliv- 
ered upon  the  street,  but  well  in  advance  of  the  laying,  seeing 
that  all  defective  pipe  is  removed ;  also  to  inspect  and  weigh 
all  iron-work  before  it  is  used. 

The  engineer  must  decide  where  and  how  much  sheathing 
shall  be  left  in  the  trench,  making  a  note  at  the  time  of  its 
exact  location  and  length,  must  decide  as  to  the  classification 
of  the  material  being  excavated,  and  must  measure  promptly 
all  material  classed  as  rock.  He  should  each  day  take  measure- 
ments necessary  to  locate  the  house-branches  as  indicated  by 
the  inspectors'  stakes.  It  is  well  to  measure  each  stretch  of 
sewer,  each  manhole  and  other  appurtenance  as  soon  as  com- 
pleted. 

The  engineer  should  see  that  the  contractor  respects  the 
rights  of  property-owners  and  keeps  the  streets  and  sidewalks 
open  where  possible,  that  the  laborers  are  efficient  and,  where 
necessary,  skilled  in  the  work  to  which  they  are  assigned,  and 
that  they  create  no  disturbance  along  the  streets  in  any  way 
for  which  the  contractor  is  responsible.  He  should  compel 
the  contractor  to  work  with  sufficient  force  and  in  such  a 
manner  as  will  lead  to  the  completion  of  the  work  in  the 
specified  time,  to  place  such  shoring  and  sheathing  as  may  be 
necessary  to  prevent  any  accidents  to  property  or  lives  or  to 


256  SEWERAGE. 

the  sewer,  to  provide  pumps  in  sufficient  number  and  of 
ample  size  to  handle  all  ground-water,  and  to  use  excavating- 
machinery  where  necessary.  In  general  he  should  see  that 
the  work  is  carried  on  by  proper  methods,  with  proper 
materials,  with  a  force  and  a  plant  satisfactory  in  both  char- 
acter and  extent,  and  that  the  inspector  enforces  his  directions 
as  to  details. 


ART.  67.     MEASUREMENTS. 

The  specifications  should  state  in  what  way  the  measure- 
ments shall  be  taken  for  each  description  of  work  or  material. 
The  measurements  so  made  for  the  final  estimate  (which  is 
the  name  customarily  given  to  the  measurements  and  calcula- 
tions on  which  is  based  the  final  payment  for  a  piece  of 
work)  should  be  accurately  and  carefully  taken  and  checked 
at  least  once,  as  should  be  the  calculations  based  thereon. 
The  engineer  should  be  able  to  swear  upon  the  witness-stand, 
as  he  may  be  called  upon  to  do,  that  the  final  estimate  is  a 
truthful  and  correct  statement  of  the  work  actually  done. 
Quantities  given  in  this  estimate  should  be  stated  in  the  units 
used  in  bidding  for  the  work. 

Measurement  of  the  sewer  laid  is  usually  made  from  centre 
to  centre  of  manholes,  flush-tanks,  etc.,  not  horizontally,  but 
parallel  to  the  sewer  (the  surface  of  the  street  being  practically 
this  in  most  cases),  no  deduction  being  made  for  branch 
specials  or  the  lengths  of  manholes.  Payment  is  sometimes 
made  uniformly  for  all  depths  of  sewer,  sometimes  varying 
with  varying  depths.  The  latter  seems  the  fairer  way,  par- 
ticularly where  some  lines  contracted  for  may  be  omitted  or 
new  ones  added.  Usually  no  changes  in  price  are  made  for 
less  differences  in  depth  than  two  feet,  the  measurement  being 
made  from  the  surface  to  the  under  side  of  sewer  or  of  foun- 
dation-platform. These  depths  are  ascertained  from  the 


OVERSIGHT  AND    MEASUREMENT   OF   WORK. 

profile,  on  which  are  plotted  the  surface  grade  and  the  sewer. 
Since  for  the  original  profile  elevations  were  in  general  taken 
at  loo-foot  intervals  only,  and  as  a  check  on  these,  the  eleva- 
tion of  the  surface  should  be  taken  and  noted  at  each  grade- 
plank  when  grade  is  being  given  for  sewer  construction. 

The  depth  of  each  manhole,  lamp-hole,  and  other  appur- 
tenance should  be  obtainable  from  the  profile,  but  as  a  check 
each  should  be  measured  with  a  levelling-rod  or  tape.  Each 
manhole,  lamp-hole,  flush-tank,  and  inlet  should  be  designated 
by  a  number,  by  which  it  is  referred  to.  It  is  almost  impos- 
sible otherwise  to  correctly  count  and  keep  track  of  these,, 
especially  the  manholes,  so  many  of  which  are  each  common, 
to  two  lines  of  sewer. 

Inlet-connections  may  be  measured  from  their  upper  end 
to  the  shoulder  of  the  branch  or  slant.     Whatever  the  limits, 
to  be  taken  they  should  be  carefully  set  forth  in  the  specifica^ 
tions. 

Rock  should  be  measured  before  excavation  in  most 
instances,  although  its  original  surface  can  often  be  judged 
afterward  by  that  showing  along  the  sides  of  the  trench.  If 
the  rock-surface  is  fairly  even  and  uniform  readings  may  be 
taken  at  intervals  of  10  feet;  but  if  it  be  uneven  and  jagged 
these  should  be,  not  at  regular  intervals,  but  wherever  neces- 
sary to  give  accurate  results.  All  measurements,  whether  of 
earth,  rock,  sewer,  or  manhole,  should  be  taken  to  tenths  of 
a  foot.  It  is  customary  to  allow  the  contractor  a  certain 
cross-section  of  trench,  and  pay  him  nothing  for  excess  exca- 
vation nor  deduct  for  a  less  area  of  section.  But  the  trench 
at  the  bottom  should  be  kept  the  full  width  called  for. 

A  final-estimate  book  should  be  kept,  in  which  is  entered 
an  exact  statement  of  each  piece  of  work  as  it  is  completed, 
but  not  before  then.  The  measurements  should  be  classified 
under  the  items  for  which  bids  were  received,  and  the  location 
of  each  given;  thus: 


258  SEWERAGE. 

8-INCH    SEWER,    8    TO    IO    FEET    DEEP. 

Location.  Length. 

From  manhole  No.  7  to  manhole  No.  &  327-3  feet 

Between  manhole  No.  8  and  manhole  No.  9         3Q.O    " 

8-INCH    X    4-INCH    Y    BRANCHES. 

Location.  Number. 

Between  manhole  No.  7  and  manhole  No.  8  13 

"     8     "         "          "     9  ii 

MANHOLES. 

No.  of  Manhole.  Location.  Depth. 

7  Main  Street,  between  Clinton  and  Madison  9.2 

8  Corner  Clinton  and  Main  streets  9.2 

A  pocket  field-book  should  be  constantly  at  hand,  in  which 
are  entered  all  measurements  taken,  the  points  of  the  begin- 
ning and  ending  of  "  sheathing  left  in  trench,"  of  sub-drains, 
of  foundations,  the  location  of  all  Y's,  the  details  and  quan- 
tities of  "  extras,"  the  location  of  underground  structures  for 
future  reference,  and  the  date  of  beginning  and  ending  of 
construction  on  each  stretch  of  sewer.  These  notes  should 
be  copied  every  evening  into  an  office-book,  since  a  loss  of 
these  data  would  be  serious  and  irreparable.  The  general 
appearance  of  such  notes  is  shown  on  page  259. 

It  is  well  also  to  have  a  pocket  copy  of  the  profile  of  each 
street,  showing  the  sewer  as  designed,  with  size,  grade,  eleva- 
tion, location  of  manholes,  flush-tanks,  and  other  appurte- 
nances. This  method  of  taking  these  data  to  the-field  for  use 
seems  to  be  more  complete  and  convenient  than  copying  them 
down  into  a  notebook. 

According  to  most  contracts  the  contractor  must  be  paid 
monthly,  and  for  this  purpose  monthly  estimates  must  be 
made  by  the  engineer.  He  should  estimate  each  month  the 
total  amount  of  each  item  completed  to  date,  from  which  is 
deducted  the  total  estimated  the  month  previous,  the  differ- 
ence being  the  amount  performed  during  the  month.  This 
method  prevents  the  carrying  ahead  or  accumulation  of  any 
errors  which  may  be  made  in  any  one  monthly  estimate,  which 
errors  are  liable  to  occur  owing  to  the  fact  that  such  estimate 


OVERSIGHT  AND   MEASUREMENT  Of    WORK.        259 


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must  often  be  made  hastily  and  simultaneously  with  the 
oversight  of  construction-work.  Uncompleted  work  must  be 
estimated  according  to  the  judgment  of  the  engineer  as 
equivalent  to  so  much  completed  work  of  the  same  class. 

For  the  final  estimate  all  measurements  as  given  in  the 
final-estimate  book  should  be  checked  with  the  field-book  and 
in  every  other  way  possible,  and  every  precaution  taken  to 
secure  absolute  absence  of  error  in  measurements  or  calcula- 
tions. As  a  check  upon  the  estimate  it  would  be  well  to 
obtain  from  the  contractor  the  bill  of  pipe,  brick,  and  iron 
used  by  him  upon  the  work,  allowance  of  course  being  made 
for  material  condemned  or  unused. 

ART.  68.     FINAL  INSPECTION. 

The  final  inspection  of  the  work  before  its  acceptance  from 
the  contractor  should  be  thorough,  and  made  by  the  engineer 
in  person  or  by  an  experienced,  trustworthy  assistant.  He 
should  enter  every  flush-tank,  manhole,  inlet,  or  other  appur- 
tenance sufficiently  large  for  this,  taking  its  dimensions,  notic- 
ing whether  the  head  or  grating  is  at  the  proper  level  and 
substantially  set,  the  brick-work  smooth,  the  form  regular, 
the  steps  properly  set  at  the  prescribed  intervals,  that  no 
ground-water  leaks  through  the  brick-work,  that  pipes  passing 
through  the  walls  are  properly  built  in  with  surrounding 
11  bull's-eyes;"  that  the  bottoms  of  manholes  are  formed  ac- 
cording to  instructions,  the  invert-channel  being  straight  or 
with  a  uniform  curve,  of  the  proper  width,  and  its  grade  uni- 
form through  the  manhole  and  of  the  proper  elevation,  and  that 
the  benches  have  the  specified  slope;  also,  if  there  are  sub- 
drains,  the  hand-holes  should  be  inspected,  and  these  as  well 
as  the  manholes  should  be  free  from  dirt.  Lamp-holes  should 
be  inspected  by  lowering  a  lamp  into  each  and  noting  whether 
it  is  straight  and  vertical,  and  by  seeing  that  the  heads  are 


OVERSIGHT  AND    MEASUREMENT   OF   WORK.         26 1 

set  according  to  specifications  and  at  the  proper  grade. 
Flush-tanks  should  be  filled  with  water  and  tested  for  tight- 
ness for  at  least  24  hours,  during  which  time  the  water-level 
in  them  should  not  lower  more  than  one  or  two  inches.  If 
automatic  flushing  apparatus  is  set  it  should  be  tested  with  a 
stream  sufficiently  small  to  fill  it  in  not  less  than  24  hours. 
To  expedite  the  test  it  can  be  rapidly  filled  and  discharged 
once  to  test  its  proper  working,  then  rapidly  filled  three 
quarters  way  to  the  discharging-point  and  the  inflowing 
stream  cut  down  to  the  rate  above  mentioned,  to  see  that  the 
siphon  does  not  "  trickle,"  but  holds  the  water  until  the 
height  is  reached  calculated  to  cause  a  complete  siphoning  of 
the  water  in  the  tank. 

Every  foot  of  sewer  and  inlet-connection  should  be  in- 
spected. Sewers  24  inches  or  over  in  diameter  should  be 
entered  and  each  joint  inspected,  if  they  are  pipe  sewers,  to 
see  that  no  jute  or  cement  protrudes  into  the  sewer  and  that 
there  is  no  leakage.  In  case  of  the  former  the  protruding 
cement  or  jute  should  be  removed;  and  if  there  is  leakage 
this  should  be  stopped,  for  which  purpose  there  may  be  calked 
into  the  joint  from  the  inside  dry  cement  immediately  fol- 
lowed by  jute,  cloth,  or  similar  material  to  hold  it  in  place 
until  set;  or  wooden  wedges,  or  tea-lead  may  be  used.  If 
these  or  similar  methods  fail  it  may  be  necessary  to  uncover 
the  pipe  and  apply  additional  cement  on  the  outside,  backed 
and  supported  by  concrete  if  necessary.  Any  cracked  or 
broken  pipe  should  be  dug  up  and  replaced.  The  branches 
should  be  examined  also  to  see  that  a  water-tight  cover  is  in 
each  one  which  is  not  already  connected  with  a  house-drain. 

If  the  sewer  is  of  brick  the  brick-work  should  be  smooth, 
with  struck  or  pointed  joints  and  without  any  cracks.  To 
determine  whether  the  form  and  dimensions  are  as  specified 
a  skeleton  templet  may  be  used.  If  the  sewer  is  circular  this 
may  consist  of  two  light  rods,  each  of  a  length  equal  to  the 


262  SEWERAGE. 

nominal  interior  diameter,  and  connected  by  a  bolt  passing- 
loosely  through  holes  at  the  exact  centre  of  each.  One  of 
these  rods  is  to  be  held  stationary  across  the  sewer  and  the 
other  revolved  upon  the  bolt,  when  each  end  of  the  latter 
should  just  touch  the  sewer  through  the  entire  revolution. 
For  an  egg-shaped  sewer  a  half  templet  may  be  used.  Slants 
or  other  branches  should  be  examined  as  stated  for  pipe 
branches.  Special  attention  should  be  paid 
to  junctions  of  brick  sewers  to  see  that  the 
curve's  are  easy  and  uniform  in  plan  and  that 
the  arches  are  strong  and  well  built.  All 
spalls,  bats,  plank,  and  other  refuse  and  dirt 
should  be  removed  from  the  sewers.  If 
brick  sewers  leak  the  joints  may  be  calked, 
as  suggested  for  pipe-sewer  joints.  For 

such  inspections  a  lantern  with  a  reflector  is 
FIG.  o. — INSPECTOR'S  j     .     ,  , 
TEMPLET  FOR  EGG-  desirable. 

SHAPED  SEWER.  Inspection  of  small  pipe  sewers  can  be 

made  from  manholes  only.  As  a  test  for  straightness  a  light 
held  at  the  opening  of  the  pipe  in  a  manhole  or  lowered  into 
a  lamp-hole  should  be  distinctly  visible  from  the  next  man- 
hole. Further  inspection  can  be  made  by  the  use  of  mirrors 
from  which  light  is  reflected  into  the  sewer.  The  simplest 
plan  is  to  reflect  the  sunlight  from  a  mirror  held  by  an  assist- 
ant on  the  surface  to  another  mirror  held  by  the  inspector  in 
the  manhole,  who  so  manipulates  his  mirror  as  to  throw  a 
spot  of  light  onto  each  length  of  the  sewer  in  succession, 
meantime  inspecting  the  same  by  looking  past  the  mirror  into 
the  sewer.  This  generally  requires  that  he  kneel  in  the  man- 
hole upon  the  side  benches,  his  back  to  the  sewer  to  be 
inspected,  his  head  bent  down  until  he  can  see  into  the  sewer, 
and  the  hand  which  holds  the  mirror  thrust  back  between  his. 
legs.  It  is  advisable  that  he  have  pads  for  his  knees  if  he 
have  many  sewers  to  inspect  in  this  way.  Apparatus  has 


OVERSIGHT  AND    MEASUREMENT  OF   WORK. 


263 


been  devised  for  removing  some  of  the  inconveniences  of  this 
method  by  so  placing  an  additional  mirror  that  the  interior 
of  the  sewer  is  reflected  therein,  and  the  inspector  is  relieved 
of  the  necessity  of  assuming  an  uncomfortable  position.  Such 
an  apparatus  is  described  in  Engineering  News,  vol.  xxxn, 
page  249. 

The  imperfections  most  commonly  found  in  pipe  sewers 
are:  loops  or  ends  of  oakum  or  ridges  of  cement  protruding 
into  the  sewer  at  the  joints;  dirt,  stones,  etc.,  in  the  sewer; 
uneven  grade,  which  can  be  detected  by  allowing  a  small 
amount  of  water  to  flow  through  the  sewer,  which  stream  will 
be  wider  at  the  depressed  and  narrower  at  the  elevated  points; 
ground-water  leaking  in  through  the  joints;  broken  pipe; 
breaks,  at  joints,  in  the  continuity  of  the  invert-surface. 

The  last  defect  can  be  remedied  by  relaying  the  pipe,  or 
by  drawing  through  the  sewer  an  "  invert-former  "  filled  with 
thin  neat  Portland-cement  mortar  (slow-setting).  This  is 
essentially  a  box,  its  bottom  of  the  shape  and  size  of  the 
sewer-invert,  through  a  large  opening  in  which  the  cement 
passes  to  the  sewer,  to  be  pressed  into  shape  by  the  rear  end 
of  the  box  as  it  passes  over  it.  The  box  is  heavily  weighted 
to  force  ahead  the  surplus  cement.  It  can  be  made  of  thin 


FIG.  10. — INVERT-FORMER. 


SECTION  ON  AB. 


sheet  iron  bent  to  the  proper  shape  and  stiffened  by  inside 
partitions  cut  from  plank.  Broken  pipe  and  leaking  joints 
can  only  be  repaired  by  digging  down  to  the  sewer  (see,  how- 
ever, Art.  85).  Dirt,  stones,  and  protruding  cement  may  be 


264  SEWERAGE. 

removed  by  drawing  a  scraper  through  the  sewer  by  means  of 
a  rope,  or  by  pushing  it  through  by  a  rod  formed  by  jointing 
together  several  shorter  rods  of  a  size  which  can  be  introduced 
through  a  manhole — about  5  feet.  A  stream  of  water  from  a 
fire-hose  nozzle  under  a  good  head  can  be  used  to  remove 
from  a  stretch  of  sewer  not  more  than  300  feet  long  almost 
anything  less  in  size  and  weight  than  a  brick.  The  hose 
while  water  is  passing  through  it  is  so  stiff  that  it  can  be 
pushed  for  a  long  distance  into  the  sewer.  Jute  ends  or 
loops  are  sometimes  difficult  to  remove,  but  can  usually  be 
cut  off  by  a  sharp  knife-blade  fastened  to  a  long  rod,  or 
burned  off  by  putting  under  them  (they  generally  hang  from 
the  top  of  the  sewer)  a  small  lamp  or  candle  similarly  fas- 
tened. Or,  if  there  is  water  flowing  through  the  pipe,  the 
candle  may  be  fastened  to  a  piece  of  wood  or  cork  to  which 
a  string  is  attached  and  floated  down  to  the  desired  point. 
The  exact  distance  from  the  manhole  of  any  defect  can  be 
ascertained  by  counting  the  number  of  pipe  intervening. 

Sub-drains  should  be  inspected  by  turning  into  each 
stretch  for  a  short  time  all  the  water  it  can  carry  (if  they  are 
not  already  running  full)  and  watching  for  indications  of 
stoppages.  The  apparatus  for  inspecting  sewers  above 
referred  to  may  in  some  instances  be  used  for  sub-drains, 
being  lowered  into  the  sub-drain  hand-hole.  If  any  drain  is 
entirely  stopped  this  may  be  remedied  by  the  use  of  rods, 
fire-hose,  "  pills  "  (see  Art.  85),  etc. ;  or  it  may  be  necessary 
to  locate  the  obstruction  and  dig  down  to  it. 

As  far  as  possible  assurance  should  be  had  by  examination 
that  all  the  conditions  of  the  contract  have  been  carried  out, 
those  having  reference  both  to  the  construction  and  to  the 
more  strictly  business  relations  between  city  and  contractor. 


CHAPTER    XIII. 
PRACTICAL   SEWER   CONSTRUCTION. 

SEWER  construction  is  sometimes  undertaken  by  the 
city  under  the  immediate  supervision  of  the  engineer,  who 
should  in  such  a  case  be  well  informed  in  practical  construc- 
tion methods.  He  would  also  be  better  fitted  by  such  infor- 
mation to  design  a  system  and  to  oversee  it  if  constructed  by 
a  contractor.  This  chapter  is  intended  to  give  some  informa- 
tion on  this  subject  based  upon  practical  experience.  It  is 
not  pretended  that  the  entire  field  is  covered,  but  it  is 
thought  that  the  student  and  those  with  little  experience  in 
sewerage-work,  and  perhaps  others,  will  find  the  information 
given  of  considerable  value. 

ART.  69.     ORGANIZING  THE  FORCE. 

The  number  of  men  which  can  be  worked  in  one  gang 
economically  depends  upon  the  character  of  soil,  depth  of 
excavation,  amount  of  ground-water,  manner  of  construction 
of  the  sewer;  also  upon  the  personality  of  the  general  foreman 
and  contractor.  If  the  soil  is  "  rotten,"  with  little  cohesion, 
very  wet,  or  the  trenches  very  shallow,  the  gangs  should  be 
small;  but  if  the  ground  is  dry  and  stands  up  well  or  the 
trenches  are  deep  larger  gangs  can  be  used.  With  the 
increase  in  the  number  of  gangs  comes  increased  difficulty  in 
keeping  them  all  supplied  with  materials  and  tools  and  work- 

265 


266  SEWERAGE. 

ing  to  an  advantage.  Good  foremen  are  a  necessity  if  there 
are  to  be  more  than  two  or  three  gangs,  since  it  may  at  times 
be  necessary  to  leave  them  to  carry  on  their  work  for  days  at 
a  stretch  with  no  more  than  a  hasty  daily  visit  from  the  con- 
tractor or  general  foreman.  A  foreman  who  can  keep  the  men 
faithfully  at  work  without  favoritism  or  making  himself  gen- 
erally hated  by  them,  who  has  sufficient  intelligent  foresight 
to  arrange  their  work  a  day  or  two  ahead,  to  never  be  out  of 
sheathing,  cement,  sand,  brick,  or  other  material,  who  has  a 
practical  knowledge  and  knack  for  overcoming  difficulties,  and 
who  can  be  depended  upon  to  be  sober  from  the  time  the 
work  starts  until  it  ends — such  a  man  is  valuable  upon  sewer- 
age-work. But  if  such  men  cannot  be  had  it  will  be  better 
to  work  only  two  or  three  gangs,  all  of  which  can  be  kept 
under  the  contractor's  or  engineer's  eye. 

The  city  engineer  or  the  contractor,  as  the  case  may  be,, 
if  he  does  not  himself  devote  his  entire  time  to  it,  should  have 
a  general  foreman  over  the  entire  work.  There  should  be  a 
foreman  over  each  gang,  and  if  the  number  in  a  gang  exceeds 
30  an  additional  foreman;  also  in  each  a  water-boy  to  carry 
drinking-water  and  run  errands.  If  the  trenches  need  sheath- 
ing there  should  be  on  each,  under  the  direction  of  the  fore- 
man, from  one  to  three  men  handy  and  experienced  in  such 
work. 

It  will  be  necessary  to  sharpen  the  picks  frequently,  even 
twice  a  day  in  flinty  hard-pan  or  gravel,  and  for  this  purpose* 
as  well  as  to  repair  shovels,  wheelbarrows,  axes,  chains,  etc.,, 
a  blacksmith  should  be  established  handy  to  the  work.  When 
not  engaged  on  such  repairs  he  can  be  making  manhole-steps, 
calking-irons,  etc. 

There  should  be  a  timekeeper,  if  the  force  is  large,  to 
take  the  time  daily  and  make  it  up  for  each  pay-day,  who 
may  also  serve  as  clerk,  keeping  account  of  all  material 
received  and  where  delivered,  ordering  new  when  so  in- 


PRACTICAL   SEWER    CONSTRUCTION.  267 

structed,  and  keeping  a  daily  account  of  the  work  done  by 
each  gang. 

Two  pipe-layers  may  be  connected  with  each  gang  if  the 
trench  can  be  rapidly  excavated ;  otherwise  two  or  more  gangs 
may  have  a  pair  of  pipe-layers  in  common,  who  lay  pipe  first 
in  one  trench  and  then  in  another,  as  sufficient  length  of  each 
is  excavated.  For  manholes,  flush-tanks,  and  other  masonry 
appurtenances  a  mason  and  two  helpers  may  work  together, 
passing  from  point  to  point  as  needed.  For  brick  sewers  two, 
four,  or  even  six  or  eight  masons  may  work  together,  the 
number  in  a  gang  usually  being  even.  The  number  of  masons' 
helpers  depends  somewhat  upon  the  depth  of  the  sewer,  one 
or  more  extra  ones  being  required  to  lower  brick  and  mortar 
if  the  depth  is  considerable.  For  a  depth  of  8  feet  or  less 
approximately  the  following  will  be  needed :  two  masons,  four 
helpers;  four  masons,  seven  helpers;  eight  masons,  fourteen 
helpers. 

Besides  the  teams  employed  in  hauling  material  to  the 
work  there  should  be  one  for  carrying  from  place  to  place 
mortar-boxes,  tool-boxes,  and  other  heavy  articles. 

It  is  difficult  to  say  anything  definite  concerning  the 
number  of  men  which  should  form  an  excavating-gang.  There 
should  be  sufficient  to  keep  the  pipe-layers  or  masons  con- 
stantly at  work.  Each  gang  or  set  of  gangs  to  which  a  pair 
of  pipe-layers  or  force  of  masons  is  assigned  should  be  just 
large  enough  to  open  and  back-fill  trench  at  the  average  rate 
at  which  the  sewer  is  laid.  If  the  sewer  frequently  varies  in 
depth  or  ease  of  digging  it  is  often  well  to  assign  a  force  of 
masons  or  pipe-layers  to  two  gangs,  always  endeavoring  to  so 
arrange  that  one  of  these  is  in  soil  rapidly  trenched  whenever 
the  other  is  in  deep  or  difficult  work.  For  8-foot  excavation 
in  good  soil  requiring  little  bracing  25  to  30  men  at  the  shovel 
is  usually  an  economical  number;  at  15  feet,  if  no  excavating- 
machinery  is  used,  60  to  80  will  be  required  for  equally  rapid 


268  SEWERAGE. 

work.  On  account  of  the  considerable  sheathing  necessary  at 
such  depths  and  for  other  reasons  it  may  be  better,  however, 
to  still  maintain  the  gang  at  25  or  30  men,  and  assign  the 
sewer-masons  or  -layers  to  two  gangs.  It  is  usually  undesir- 
able to  change  the  size  or  personnel  of  gangs  after  they  have 
once  been  gotten  into  good  working  shape. 

If  a  trench  runs  into  very  wet  soil  or  quick  or  running 
sand  gangs  as  large  as  the  above  cannot  be  used  to  advantage, 
since  not  only  must  sheathing  be  set  and  driven  right  up  to 
the  excavation  as  it  proceeds,  but  the  pipe  or  sub-drain  must 
be  laid  or  foundation  put  in  foot  by  foot  as  the  bottom  of  the 
trench  is  reached;  also  an  upheaval  of  the  quicksand  bottom, 
caving,  and  other  accidents  may  cause  occasional  stoppages  of 
the  work  for  a  few  minutes,  when  almost  the  entire  gang 
must  lie  idle  or  go  to  back-filling.  In  such  difficult  work  on 
pipe  sewers  a  gang  may  consist  of  a  foreman,  a  sheather,  two 
pipe-layers,  and  five  or  six  laborers.  If  the  ground  is  very 
wet  it  is  advisable  to  open  only  a  little  trench  at  a  time,  since 
the  more  that  is  open  below  water-level  the  greater  the 
amount  of  water  which  will  flow  through  the  trench  and  inter- 
fere with  the  work.  Under  such  circumstances  the  gangs 
should  be  small. 

If  the  back-filling  is  not  to  be  rammed  it  is  the  custom  of 
many  contractors  to  use  the  entire  gang  for  the  last  20  to  30 
minutes  each  day  in  back-filling.  This  arrangement  has  the 
advantage  of  not  requiring  an  extra  gang  and  foreman  for 
back-filling.  But  if  there  are  three  or  more  gangs  excavating 
it  would  perhaps  be  better  to  keep  one  gang  continually  back- 
filling. This  is  certainly  advisable  in  all  cases  where  the 
trench  is  to  be  thoroughly  tamped. 

The  contractor,  general  foreman,  or  timekeeper  should 
visit  each  gang  just  after  the  beginning  and  just  before  the 
ending  of  each  day's  work,  at  the  least,  to  learn  of  any 
material  needed  or  difficulty  encountered,  and  also  to  get  th? 


PRACTICAL   SEWER    CONSTRUCTION.  269 

"  time  "  of  the  men,  which  may  have  been  taken  by  the  fore- 
man, or  may  better  be  taken  directly  by  one  of  the  three 
above  mentioned. 

If  Italians  or  other  non-resident  workmen  be  employed 
(and  if  the  work  is  in  a  small  city  and  requires  many  men 
outside  labor  must  be  obtained)  they  are  usually  housed 
together  in  barns  or  empty  houses  or  shanties  constructed 
for  the  purpose  on  the  outskirts  of  the  city.  If  these  can  be 
located  near  a  stream  the  men  will  usually  take  advantage  of 
the  opportunity  to  wash  themselves  and  their  clothes  and  keep 
in  better  health  than  if  otherwise  situated.  The  necessity  for 
walking  a  long  distance  to  and  from  work  will  result  in 
decreased  energy  in  their  labor,  and  should  be  avoided.  It 
will  sometimes  pay  to  have  the  teams  carry  them  to  and  from 
the  work.  It  will  also  be  to  the  contractor's  advantage  to  see 
that  their  food  is  wholesome.  A  considerable  experience  with 
Italian  laborers  has  convinced  the  author  that  as  a  class  they 
are  more  appreciative  than  are  native  laborers  of  both  kind- 
ness and  harsh  treatment,  and  are  shrewd  readers  of  motives 
of  conduct.  If  justly  though  firmly  treated  they  are  polite, 
obedient,  and  good  workers,  slow  to  wrath,  but  dangerous  if 
ill  treated.  "  Sore-heads  "  among  them  should  be  gotten  rid 
of  at  once. 

Pay-days  should  come  at  as  long  intervals  as  possible, 
because  of  the  diminished  force  which  can  be  made  to  work 
for  the  following  day  or  two,  if  for  no  other  reason.  For  some 
reason  masons  seem  to  be  peculiarly  subject  to  the  failing  of 
"  pay-day  drunks,"  and  if  possible  an  arrangement  should  be 
made  with  them  to  pay  their  expenses  wherever  they  wish  to 
board  and  a  small  weekly  amount  of  pocket-money,  the 
balance  being  paid  them  when  their  work  is  completed. 
Monthly  payments  are  generally  made  to  the  laborers,  imme- 
diately after  the  payment  of  the  monthly  estimates. 


2/0  SEWERAGE. 

ART.  70.     TRENCHING  BY  HAND. 

The  line  of  the  trench  being  given  by  centre  stakes,  the 
sides  of  the  excavation  are  indicated  by  measuring  the  proper 
distance  on  each  side  of  the  stakes  and  stretching  sash-cord 
or  clothes-line  there  and  marking  the  ground  along  this  line 
by  means  of  a  pick.  The  laborers  are  then  placed  at  regular 
intervals  along  the  trench,  varying  from  6  to  20  feet,  in  single 
line  in  most  cases,  but  if  the  trench  is  8  feet  or  more  wide 
they  may  be  in  double  line.  It  may  be  well  to  define  in  some 
way,  as  by  a  mark  in  the  ground  or  stake  at  one  side  of  the 
trench,  equal  lengths  of  trench,  one  man  being  required  to 
work  within  the  limits  of  each  length.  Where  possible  it  is 
desirable  that  this  length  be.  that  which  can  be  completed  in 
a  half  or  a  whole  day. 

If  the  street  is  macadamized  or  gravelled  or  has  a  hard  dirt 
surface  a  contractor's  "  rooter  plow"  may  be  used  to  break 
the  surface;  but  this  is  not  advisable  in  narrow  trenches,  nor 
should  the  surface  be  broken  beyond  the  sides  of  the  trench, 
since  if  sound  it  helps  to  prevent  caving  of  the  sides. 

If  there  is  any  paving  material  on  the  street  it  should  be 
thrown  upon  one  side  of  the  trench,  and  the  remaining 
excavated  material  upon  the  other  side,  the  material  on  each 
side  being  kept  back  a  foot  or  two  from  the  edge  of  the  trench 
to  allow  a  pathway  for  foremen  and  inspector  and  for  lowering 
material,  but  still  more  to  prevent  excavated  material  from 
falling  back  into  the  trench.  Thus  one  side  of  the  street  is 
left  open  to  travel,  the  pile  of  paving  material  acting  as  a  guard 
to  the  trench  on  that  side.  If  so  much  soil  is  to  be  thrown 
out  or  the  street  is  so  narrow  that  it  cannot  all  be  placed  upon 
one  side  of  the  trench  it  may  be  placed  upon  both  sides,  the 
paving  material  being  kept  separate,  say  along  the  outside 
edge  of  one  bank;  but  it  would  be  better  to  use  excavating- 
machinery  and  thus  avoid  blocking  the  street  entirely.  The 


PRACTICAL    SEWER    CONSTRUCTION.  2JI 

amount  which  can  be  placed  upon  one  side  of  the  street  with- 
out covering  the  sidewalk  may  be  increased  by  setting  there 
a  platform  and  guard,  as  shown  in  Fig.  n. 

The  first  earth  cast  out  should  be  thrown  to  what  will  be 
the  outside  edge  of  the  bank,  since  it  cannot  be  thrown  there 
when  the  trench  is  deeper  without  double  handling.  The 
gutters  should  be  kept  open  and  free  from  any  excavated 
material.  Down  to  a  depth  of  9  to  12  feet  the  earth  can  be 
cast  to  the  surface,  although  after  5  or  6  feet  is  reached  it  will 


FIG.  ii.— EXCAVATION-PLATFORM. 

be  necessary  to  keep  additional  men  on  the  surface  to  throw 
back  onto  the  pile  the  material  so  cast  out.  When  the  depth 
exceeds  9  to  12  feet  it  will  be  necessary  to  handle  the  material 
twice  before  it  reaches  the  surface,  by  placing  a  platform  or 
staging  about  6  or  7  feet  below  the  surface,  onto  which  the 
earth  is  thrown  by  two  to  four  men,  and  from  which  it  is 
thrown  to  the  surface  by  one  man.  If  the  depth  exceeds  16 
or  1 8  feet  still  another  platform  will  be  necessary  about  7  or 
8  feet  below  the  first.  These  platforms  are  usually  made  by 
resting  plank  upon  the  braces  or  rangers  of  the  sheathing. 
(Except  in  rock  cuts  there  are  almost  no  conditions  under 
which  a  trench  10  feet  or  more  in  depth  should  be  left 
unbraced.)  The  platform  may  consist  of  short  pieces  of  plank 
placed  crosswise  of  the  trench,  their  ends  resting  on  the 
rangers,  or  of  long  plank  lengthwise  of  the  trench  resting  upon 
the  braces.  The  latter  cannot  well  be  used  if  the  trench  is 


2/2 


SEWERAGE. 


less  than  5  feet  wide,  but  is  the  better  form  for  wide  trenches. 
If  there  is  more  than  one  tier  of  longitudinal  platforms  the 
successive  tiers  should  be  placed  alternately  upon  opposite 
sides  of  the  trench;  or  if  cross-platforms  are  used  the  right 
side  of  one  should  be  vertically  above  the  left  side  of  the  next 
lower,  alternate  platforms  being  vertically  above  each  other. 
The  number  of  men  excavating  which  cast  onto  one  platform 


FIG.  12. — CROSS-STAGING  IN  TRENCH. 

may  be  only  two,  but  should  increase  with  the  difficulty  of 
excavating,  so  as  to  keep  the  staging-man  busy. 

Where  it  is  allowed  (as  it  is  in  many  cities),  and  the  trench 
is  over  10  feet  deep,  it  is  often  economical,  except  in  hard 
rock,  dry  sand,  or  quicksand,  to  make  the  excavation  in  alter-, 
nate  tunnels  and  open  trenching,  the  sections  of  each  being  8 
to  20  feet  long.  The  tunnel  is  usually  made  about  5  feet 
high.  The  amount  of  material  to  be  removed  and  of  bracing 
to  be  put  in  is  thus  reduced.  But  tunnelling  should  never  be 
allowed  under  streets,  except  in  rock,  unless  the  tunnel  is 
afterwards  opened  and  back-filled  as  open  trench,  being  used 
only  to  save  bracing;  since  it  is  practically  impossible  to  so 
compact  the  back-filling  in  a  tunnel  as  to  prevent  future 
settlement,  which  may  not  occur,  however,  until  months  or 
years  later,  when  the  contractor  has  been  relieved  of  all 


PRACTICAL   SEWER    CONSTRUCTION.  2/3 

responsibility.  Where  the  amount  of  traffic  on  a  street  or 
other  conditions  require  it,  however,  a  tunnel  may  be  run 
under  the  street  and  a  masonry  lining,  which  may  be  the 
sewer  itself,  built  against  the  outside  of  the  excavation,  so 
that  there  is  no  back-filling  except  in  the  form  of  masonry; 
which  construction  requires  special  tunnelling-machinery  and 
methods.  In  Paris  by  the  use  of  a  shield  a  tunnel  19  feet 
outside  diameter  was  run  with  a  covering  in  some  places  of 
only  2  feet  between  it  and  the  street-paving  above,  without 
causing  any  cracks  in  the  latter.  The  successful  tunnelling 
for  the  Boston  underground  railway  is  familiar  to  all.  A 
notable  instance  of  sewer-tunnelling  is  found  in  the  sewers 
tunnelled  through  sand-rock  at  St.  Paul,  Minn.,  the  tunnel, 
when  lined  on  the  bottom,  constituting  the  sewer.  Restric- 
tions against  tunnelling  should  not  of  course  apply  to  lines 
whose  depth  is  75  feet  or  more,  such  as  those  passing  through 
ridges. 

There  is  a  tendency,  if  a  right-handed  laborer  always  faces 
one  way  while  picking,  for  the  trench  to  work  to  his  left  as  it 
descends.  He  should  be  taught  to  avoid  this  by  keeping  his 
left  side  to  the  side  of  the  trench  at  which  he  is  picking,  so 
that  both  sides  shall  make  the  same  angle,  if  any,  with  the 
vertical. 

It  pays  to  keep  the  picks  sharpened  and  good  shovels  in 
the  men's  hands.  For  this  purpose  there  should  be  25  to  100 
per  cent  more  picks  than  laborers,  to  allow  opportunity  for 
sharpening  them.  For  digging  the  round-pointed  shovel  is 
best,  but  staging-men  and  mortar-mixers  should  use  square- 
pointed  shovels.  There  should  be  a  few  extra  shovels  con- 
stantly on  hand,  including  a  few  long-handled  ones,  but  these 
latter  should  not  be  used  for  trenching  except  in  deep 
trenches  where  the  shovelling  is  very  easy. 

In  soil  where  caving  is  frequent  and  sheathing  is  not  used 
the  trench  should  be  refilled  as  soon  as  possible,  since  the 


274  SEWERAGE. 

longer  it  stands  the  greater  the  probability  of  caving.  Soils, 
such  as  clay  or  other  heavy  ground,  having  some  cohesion 
will  usually  give  warning  of  caving  by  cracking  a  few  feet  back 
from  the  edge  of  the  trench,  and  should  be  braced  as  soon  as 
such  sign  appears.  Gravelly  soils  or  dry  sand  usually  give  no 
such  warning,  and  are  particularly  dangerous  on  this  account 
and  because  they  may  bury  and  suffocate  the  men;  while 
clay,  coming  in  lumps,  although  it  may  bury  and  even  crush 
them,  will  permit  them  to  breathe  until  they  can  be  rescued. 
Trenches  in  gravelly  and  sandy  soil  should  always  be  sheathed. 

If  a  boulder  is  met  with  it  may  be  raised  from  the  trench 
by  a  derrick  or,  if  too  large  for  this,  may  be  blasted.  Before 
blasting  the  earth  should  be  removed  from  all  sides  of  the 
boulder  and  the  trench  in  the  vicinity  should  be  braced.  It 
may  sometimes  be  cheaper  to  dig  a  hole  in  the  side  of  the 
bank  and  roll  the  boulder  into  this  out  of  the  way.  In  some 
cases,  when  the  sewer  would  pass  entirely  under  the  boulder, 
this  may  be  left  undisturbed  and  tunnelled  under.  If  it 
merely  protrudes  into  the  trench  a  portion  may  be  removed 
by  "  feathers  and  wedge  or  a  heavy  sledge. 

If  a  water-  or  gas-pipe  or  other  conduit  run  diagonally 
across  a  trench,  or  run  in  it,  or  cross  one  more  than  8  or  10 
feet  wide,  it  should  be  supported  in  position  before  the  earth 
is  removed  from  under  it.  This  can  be  done  by  placing 
across  the  trench  at  intervals  of  12  feet  sufficiently  strong 
timbers  or  old  rails,  and  suspending  the  conduit  from  these 
by  chains  drawn  tight  by  driving  wedges  between  them  and 
the  beams.  Rope  should  not  be  used  for  this  purpose,  as 
rain  causes  it  to  contract  or  break  in  the  attempt  to  do  so. 
If  such  a  pipe  lies  in  the  bank,  close  to  or  slightly  protruding 
into  the  trench,  the  bank  should  be  thoroughly  braced  just 
under  the  pipe  and  the  pipe  itself  be  held  in  place  by  braces. 
These  braces  should  not  be  removed  when  the  trench  is  back- 
filled, and  if  the  pipe  is  suspended  the  trench  should  be  filled 


PRACTICAL   SEWER    CONSTRUCTION.  2?$ 

and  thoroughly  tamped  under  and  around  the  pipe  before  the 
chains  are  removed.  The  breaking  of  a  water-main  in  or  near 
a  sewer-trench  is  one  of  the  most  disastrous  accidents  which 
can  happen  to  it.  Small  house-connection  pipes  crossing  the 
trench  are  apt  to  be  broken  by  workmen  climbing  over  them 
and  should  be  protected,  as  by  a  piece  of  plank  or  of  a 
2X4  placed  across  the  trench  just  above  such  pipe,  the 
ends  extending  6  inches  or  more  into  the  banks  for  support. 
In  all  cases  where  there  is  danger  from  water-pipe  such  and 
so  many  gates  should  be  temporarily  closed  that  the  closing 
of  only  one  more  will  entirely  shut  off  the  pressure  from  the 
threatening  line  of  pipe,  and  a  wrench  be  kept  at  hand  for 
closing  this. 

If  a  drain  crosses  the  trench  the  pipe  should  be  removed 
and  saved,  and  a  trough  substituted  during  construction,  its 
ends  supported  in  the  banks.  The  back-filling  should  be 
carefully  tamped  under  this  and  the  pipe  relaid  in  the  trough. 

At  the  first  sign  of  quicksand  the  best  of  close  sheathing 
should  be  at  once  -put  in,  an  experienced  foreman  put  over 
this  work  and  the  best  men  placed  upon  it  (see  Art.  72). 

The  soil  where  a  trench  has  previously  been  dug,  although 
it  were  years  before,  is  more  liable  to  cave  than  that  which 
has  never  been  disturbed,  and  the  sewer-trench  should  be 
kept  several  feet  from  such  old  trench  if  possible. 

ART.    71.       EXCAVATING-MACHINERY. 

As  a  general  statement  it  may  be  said  that  it  does  not  pay 
to  use  any  kind  of  machinery  in  excavating  where  the  trench 
is  less  than  8  or  9  feet  deep  or  wide,  although  it  may  be 
desirable  or  necessary  to  do  so  where  for  some  reason  the 
excavated  material  cannot  be  piled  along  the  side  of  the 
trench.  The  advantages  attending  the  use  of  machinery  are: 
greater  amount  of  material  excavated  with  a  given  number  of 


SE  WERA  GE. 

men,  less  danger  of  caving  of  banks  from  the  weight  of  earth 
piled  upon  them,  less  obstruction  to  street  traffic,  the  con- 
venience of  having  at  hand  means  for  raising  boulders,  lower- 
ing heavy  pipes,  or  other  material.  Each  of  these  advantages 
increases  in  force  with  the  depth  of  the  sewer.  With  several 
of  the  machines  now  on  the  market  the  cost  of  handling 
material  increases  but  little  with  the  depth.  The  machinery 
in  use  varies  from  an  ordinary  boom-derrick  to  an  elaborate 
system  of  trestles,  wire  ropes,  and  buckets,  which  may  stretch 
along  400  feet  or  more  of  trench. 

For  a  large  brick  sewer  a  handy  arrangement  is  that  of  two 
derricks  with  booms  about  40  feet  long,  both  placed  on  the 
same  side  of  the  trench  and  about  75  feet  apart.  Both  boom- 
and  main-falls  should  wind  upon  drums  driven  by  steam- 
power.  With  this  arrangement  a  bucket  of  earth  can  be 
hoisted  from  the  excavation  and,  passing  from  one  derrick  to 
another,  be  deposited  in  the  trench  125  or  even  145  feet 
away.  This  plan  is  not  adapted  to  narrow  trenches  nor  to 
those  where  any  considerable  length  of  trench  is  to  be  under 
excavation  at  one  time.  For  these  one  of  the  trestle-machines 
or  cable-ways  is  preferable,  the  former  more  particularly  for 
trenches  up  to  12  or  15  feet  in  width,  the  latter  for  wider 
ones  and  for  particular  cases,  such  as  crossings  of  railroad- 
tracks. 

The  cable-way  consists  essentially  of  a  wire  cable  sus- 
pended over  the  centre  of  the  trench,  on  which  run  one  or 
more  travellers  carrying  buckets;  the  earth  being  excavated 
at  one  point  and  cast  into  the  buckets,  which  are  raised  and 
carried  to  the  other  end  of  the  cable,  where  they  dump  the 
earth  upon  the  completed  sewer.  It  is  essential  to  the  safety 
of  the  laborers  that  the  cable  be  most  substantially  anchored 
at  the  ends,  and  that  it  be  amply  strong  to  carry  any  load 
which  can  possibly  come  upon  it.  The  anchorage  is  usually 
in  the  shape  of  a  "  dead-man,"  but  the  ordinary  log  placed 


PRACTICAL   SEWER    CONSTRUCTION. 


277 


^iW:> 


278  SEWERAGE. 

in  the  trench  and  covered  with  earth  back-filling  should  not 
be  relied  upon.  Rock  may  be  piled  in  front  of  and  over  the 
log,  but  a  better  plan  is  to  bury  in  the  trench  a  platform  of 
stout  timber,  inclined  backward  about  45°  from  the  vertical, 
to  which  the  cable  is  fastened.  The  hoisting-  and  conveying- 
ropes  are  driven  by  an  engine  located  at  one  end  of  the  cable. 
Like  derricks,  the  cable-way  is  not  adapted  to  trenches  which 
move  forward  rapidly,  as  the  moving  and  resetting  of  it  take 
considerable  time  and  labor. 

In  the  trestle-machine  the  buckets  travel  upon  an  over- 
head track  which  is  supported  at  intervals  by  trestles  spanning 
the  trench.  Generally  from  6  to  20  buckets  are  in  use  at 
once,  one  half  of  which  are  being  filled  while  the  remainder 
are  being  carried  to  the  dump  and  emptied.  In  some  ma- 
chines the  track  forms  a  long  loop,  one  side  of  which  is  for 
going  and  the  other  for  returning  buckets.  There  are  then 
three  sets  of  buckets,  one  going  to  the  dump,  one  returning, 
and  one  set  being  filled.  To  obtain  the  greatest  efficiency  of 
the  machine  the  number  of  men  casting  into  each  bucket 
should  be  just  sufficient  to  fill  it  during  the  time  occupied  in 
removing,  emptying,  and  returning  a  set  of  buckets. 

Such  machinery  is  economical  when  the  cost  of  running — 
including  all  labor  but  that  of  the  men  digging  in  the  trench 
— and  of  repairs,  plus  the  rental  or  interest  on  first  cost  of  the 
.machine,  is  less  than  the  cost  of  "  staging  "  it  out  (as  the  use 
of  platforms  is  called)  plus  that  of  back-filling.  If  the  back- 
filling is  to  be  hand-tamped  this  last  item  should  not  be  in- 
cluded, since  if  a  machine  is  used  the  material  must  be  spread 
after  dumping.  A  good  trench-machine  is  usually  economical 
when  either  depth  or  breadth  of  trench  exceeds  8  to  10  feet 
in  ground  capable  of  rapid  trenching;  but  this  economical 
least  dimension  increases  with  the  decrease  in  the  rapidity  of 
excavation  possible.  Where  for  some  reason  the  excavation 


PRACTICAL   SEWER    CONSTRUCTION.  2/9 

can  proceed  but  slowly  the  use  of  machinery  is  not  advisable 
for  economical,  though  it  may  be  for  other,  reasons. 

Whatever  the  machinery  employed  it  should  work  suc- 
cessfully although  the  sheathing  extend  at  least  6  feet  above 
the  surface  along  each  side  of  the  trench,  should  be  able  to 
drop  a  bucket  anywhere  in  the  trench,  each  bucket  being 
always  under  perfect  control,  and  no  cable  or  rope  should 
hang  within  6  feet  of  the  ground.  It  is  better  that  it  should 
have  no  cross-ties  or  other  parts  extending  across  the  trench 
within  6  feet  of  the  ground,  and  that  it  should  not  obstruct 
the  street  for  more  than  2  feet  on  each  side  of  the  trench. 

For  deep  trenching  through  city  streets  the  use  of  exca- 
vating-machinery  is  strongly  recommended  as  of  advantage  to 
both  city  and  contractor. 

Most  makes  of  excavating-machinery  can  be  either  rented 
or  bought.  For  a  village  or  small  city  the  former  is  generally 
preferable  if  the  work  on  which  it  is  to  be  used  can  be  pushed. 
But  if  it  will  be  needed  for  more  than  one  season  it  may  be 
preferable  to  buy  instead. 

Probably  the  best-known  and  most  extensively  used 
trenching-machinery  are  the  Carson,  of  Boston,  Mass.,  and 
the  Moore,  of  Buffalo,  N.  Y.  Other  machines  are  described 
in  Engineering  Record,  vol.  XVI,  page  123,  vol.  XXXIII,  page 
100;  and  in  Engineering  News,  vol.  XXIV,  page  268,  vol. 
xxv,  page  547,  vol.  xxxvn,  page  50. 

ART.  72.     SHEATHING. 

Just  when  a  trench  can  be  relied  upon  to  stand  without 
sheathing  and  when  it  cannot  is  something  that  only  experi- 
ence can  teach.  Sheathing  is  expensive,  but  not  so  expensive 
as  excavating  a  trench  which  has  begun  to  cave,  to  say  noth- 
ing of  settling  for  injuries  and  death  of  laborers.  If  earth  has 
been  piled  upon  a  bank  which  afterwards  caves  it  may  be 


280  SEWERAGE. 

necessary  to  re-excavate  more  material  than  all  that  which 
would  have  been  excavated  had  no  caving  occurred,  and  all 
of  this  must  be  removed  to  some  distance  because  there  is  no 
bank  upon  which  to  pile  it.  Not  only  that,  but  the  soil  is 
liable  to  continue  to  slide  into  the  trench,  making  it  almost 
impossible  to  keep  the  bottom  uncovered.  If,  after  caving 
has  begun,  sheathing  is  used  the  difficulty  of  placing  it  is 
greatly  increased.  A  trench  which  if  sheathed  would  have 
given  no  trouble  may  become  a  most  discouraging  hole  into 
which  many  times  the  cost  of  sheathing  must  be  placed  in  the 
form  of  labor  before  the  sewer  is  built  therein.  The  author's 
experience  has  been  that  it  does  not  pay  to  take  many 
chances  with  unsheathed  trenches.  He  would  use  at  least 
skeleton  sheathing  in  every  trench  more  than  8  or  10  feet 
deep,  in  any  trench  in  gravelly  and  sandy  soil,  and  whenever 
the  least  sign  of  caving  appears.  Wherever  the  street  is  paved 
a  plank  should  be  placed  horizontally  on  each  side  of  the 
trench  about  6  inches  below  the  surface,  and  braces  driven 
between  these  not  more  than  6  feet  apart. 

Sheathing  is  usually  placed  as  follows:  A  plank  (a,  Fig. 
13)  is  placed  upright  in  the  trench  against  the  bank,  another 
(U)  12  feet  from  this,  and  two  against  the  other  bank  and 
directly  opposite  these.  Against  each  two  and  near  the 
street-surface  is  placed  a  horizontal  ranger  (cd  and  <?/),  both 
at  the  same  level,  and  between  them  at  each  end  a  brace  is 
driven,  long  enough  to  be  a  tight  fit.  Two  other  rangers  {gh 
and  £/)  are  placed,  one  on  each  side  of  the  trench,  from  4  to 
6  feet  below  the  others,  and  braced.  Sometimes  these  lower 
rangers  are  placed  first.  The  ends  of  the  rangers  come  in  the 
middle  of  the  uprights,  the  braces  only  an  inch  or  two  from 
the  ends  of  the  rangers.  The  next  set  of  rangers  abut  against 
these  and  are  braced  in  the  same  way.  Generally  an  addi- 
tional upright  and  braces  are  placed  midway  of  each  ranger* 
This  forms  skeleton  sheathing. 


PRACTICAL    SEWER    CONSTRUCTION. 


281 


If  the  sheathing  is  to  be  close,  plank  are  slipped  behind 
the  rangers  and  in  contact  with  each  other,  and  one  or  more 
additional  braces  are  placed  at  equal  intervals  between  each 
tier  of  rangers.  For  bracing  only,  the  rangers  and  braces  are 
used  without  any  vertical  sheathing.  These  are  ordinarily 
placed  a  foot  or  two  from  the  surface,  or  just  beneath  and  in 


FIG.  13.— SKELETON  SHEATHING. 

front  of  an  exposed  water-main  or  other  conduit.  When  a 
series  of  rangers  and  braces  are  placed  one  just  below  the 
other  horizontal  sheathing  is  formed. 

As  the  trench  is  deepened  the  sheathing  should  be  driven 
so  that  its  lower  end  is  as  near  as  possible  to  the  bottom  of 
the  trench,  unless  rock  or  some  firm  soil  be  previously 
reached.  In  quicksand  or  running  sand  the  bottom  of  the 
sheathing  should  always  be  kept  at  least  one  foot  below  the 
bottom  of  the  excavation.  This  is  essential  if  the  work  is  to 
be  done  without  considerable  loss  of  money  and  perhaps  of 
life.  As  many  men  as  are  necessary  to  insure  this  should  be 
kept  constantly  at  work  driving  the  sheathing.  No  two  planks 
behind  the  same  ranger  should  be  driven  at  once,  as  the  latter 
would  in  that  case  be  apt  to  follow  them  down,  which  it 
should  not  do. 

If  there  is  a  tendency  for  the  sheathing  to  be  forced  in  at 


282  SEWERAGE. 

the  bottom  by  the  bank,  as  in  the  case  of  quick  or  running 
sand,  a  set  of  rangers  and  braces  should  be  put  in  place  im- 
mediately under  the  lowest  set  already  in  position  as  soon  as 
the  excavation  is  low  enough  to  permit  it.  As  the  excavation 
and  sheathing  are  carried  down  this  last  set  of  rangers  should 
be  driven  down,  always  being  kept  level  crosswise  of  the 
trench  and  just  above  its  bottom,  until  it  is  the  proper  dis- 
tance below  the  preceding  set,  when  it  is  driven  no  further, 
but  another  set  is  started  under  it.  If  the  bank  is  tolerably 
stable  the  stiffness  of  the  sheathing-plank  can  be  relied  upon 
to  keep  it  in  place  below  the  second  ranger  until  the  trench 
is  sufficiently  deep  to  permit  placing  the  third  ranger  in  its 
proper  position  without  any  further  driving. 

Each  brace  should  be  exactly  beneath  the  braces  in  the 
tiers  above. 

There  is  considerable  friction  between  the  sheathing  and 
the  bank  on  one  side  and  rangers  on  the  other,  and  after  two 
sets  of  rangers  are  in  the  driving  becomes  quite  difficult  and 
the  upper  ends  of  the  plank  become  battered  and  broomed 
and  the  plank  broken,  sometimes  even  when  they  are  pro- 
tected by  caps.  Ordinarily  10  or  12  feet  is  the  greatest  depth 
to  which  plank  can  be  driven  economically.  It  then  becomes 
necessary  to  start  a  new  course  of  sheathing,  which  is  placed 
inside  the  upper  course,  its  back  resting  against  the  rangers 
of  this.  The  second  course  is  driven  and  held  in  place  by 
rangers  and  braces  as  was  the  other,  and  may  be  succeeded 
by  one  or  more  other  courses  each  10  or  12  feet  high.  When 
a  new  course  of  sheathing  is  started  it  is  advisable  to  tem- 
porarily fasten  planks  horizontally  in  front  of  and  behind  this 
sheathing  near  the  top,  by  a  nail  at  each  end  driven  into  a 
sheathing-plank,  to  keep  the  plank  in  line  and  steady  them 
while  driving. 

In  placing  each  course  after  the  first  one  an  opening  must 
be  left  at  each  vertical  line  of  braces,  since  the  sheathing 


PRACTICAL   SEWER    CONSTRUCTION. 


283 


cannot  be  driven  there.  If  these  openings  give  trouble  they 
may  be  closed  by  slipping  into  them,  behind  the  rangers, 
5 -foot  lengths  of  plank  when  the  trench  has  reached  that  dis- 
tance below  the  first  course  of  sheathing,  and  driving  these 
to  keep  pace  with  the  other  sheathing.  When  the  trench  is 
5  feet  deeper  still  another  5 -foot  length  of  plank  may  be 
slipped  behind  the  ranger  on  top  of  the  former  length,  and 
so  on.  A  short  piece  of  plank,  at  least,  should  be  kept  in 
the  bottom  of  this  opening  to  keep  the  planks  on  either  side 
the  proper  distance  apart. 

Another  method  of  closing  these  openings  is  to  cut  a  plank 
just  long  enough  to  reach  from  the  bottom  of  one  ranger  to 


-irnmrrrm 


FIG.  14. — SHEATHING  UNDER  BRACES. 

the  top  of  the  next  and  a  little  wider  than  the  opening. 
This  is  placed  over  the  opening  against  the  face  of  the  sheath- 
ing, and  between  the  rangers,  to  which  blocks  are  nailed  to 
hold  it  in  this  position  (see  Fig.  14). 

In  some  cases  it  will  not  do  to  leave  this  space  open  for 
even  a  foot  above  the  bottom  of  the  trench,  as  in  quicksand. 
It  may  then  be  advisable  .to  use  a  somewhat  different  system 
of  rangers,  as  follows:  In  placing  rangers  for  the  first  course 
of  sheathing,  where  one  ranger  is  ordinarily  placed  two  will 
be  placed,  one  in  front  of  the  other  but  separated  from  it  by 
a  small  piece  of  plank  at  the  end  of  each  brace.  The  front 
ranger  may  be  but  a  2-inch  plank.  The  second  course  of 


284  SEWERAGE. 

sheathing  is  slipped  between  the  two  rangers  and  when  it  is 
all  in  place  except  where  the  spacing-blocks  interfere  the 
braces  are  driven  along  about  a  foot,  the  spacing-blocks 
knocked  out,  and  sheathing  dropped  into  the  spaces  they 
occupied.  Generally  plank  behind  a  brace  cannot  be  driven, 
owing  to  the  friction,  but  when  the  one  next  to  it  has  been 
driven  the  brace  can  be  moved  over  in  front  of  this  and  the 
former  then  driven. 

Where  there  is  more  than  one  course  of  sheathing,  or 
whenever  the  bottom  of  any  course  is  not  kept  at  the  bottom 
of  the  trench,  all  braces  in  each  vertical  line  should  be  tied 
together  by  cross-bracing  of  plank  nailed  to  them ;  otherwise 
one  side  of  the  sheathing  may  drop,  loosening  the  braces  and 
causing  a  complete  collapse  of  sheathing  and  trench.  The 
author  has  seen  several  serious  accidents  due  to  the  neglect 
to  use  such  cross-bracing. 

The  sheathing  is  usually  of  hemlock  plank,  although  pine 
would  be  better,  being  less  brittle.  Maple  and  other  hard 
wood  has  been  used  in  a  few  instances.  The  plank  is  usually 
2  inches  thick,  although  heavier  may  be  advisable  in  deep, 
wide  trenches  or  where  it  is  desirable  to  use  as  few  rangers 
and  braces  as  possible.  It  should  never  be  less  than  2  inches 
thick.  Ten  or  12  feet  is  the  usual  length,  although  18  or  more 
is  sometimes  used.  But  the  great  amount  of  friction  between 
such  long  plank  and  the  earth  makes  it  extremely  difficult  to 
drive  the  last  6  or  8  feet,  the  top  of  the  plank  being  usually 
broomed  or  broken  in  the  attempt.  For  the  same  reason  the 
width  of  the  plank  does  not  usually  exceed  6  or  8  inches. 
All  the  sheathing  in  a  given  course  should  be  of  approxi- 
mately the  same  length.  Sheathing-plank  should  be  sharp- 
ened to  a  chisel  edge,  the  flat  side  being  placed  against  the 
bank,  and  the  edge  which  will  not  be  in  contact  with  the 
plank  last  driven  should  be  bevelled,  that  the  plank  may  hug 
the  bank  and  keep  a  close  joint  with  the  one  previously 


PRACTICAL   SEWER   CONSTRUCTION. 


285 


driven.  The  bevel  may  be  3  to  5  inches  long.  The  top  of 
the  sheathing-plank  should  be  bevelled  on  each  edge,  to 
lessen  splitting  and  binding  and  to  permit  of  using  a  driving- 
cap,  which  is  advisable  if  the  sheathing  drives  hard,  to  keep 
the  plank  from  brooming. 

For  driving  the  sheathing  a  hardwood  maul  is  ordinarily 


u 


6- 


il 

J 

f»9 
"i 
1 

I 

FIG.  15.— DRIVING-CAP  AND  MAUL. 

used,  about  6  inches  in  diameter  and  15  inches  long,  with  a 
wrought-iron  hoop  banding  each  end. 

If  a  large  amount  of  sheathing  is  to  be  driven  in  deep 
trenches  a  steam-hammer  pile-driver  may  be  used  to  advan- 
tage. This  does  not  broom  the  pile,  and  by  using  it  sheath- 
ing 1 8  feet  long  or  more  may  be  driven.  It  is  particularly 
applicable  to  sand  and  elastic  soils. 

If  the  ground  is  such  as  to  require  sheathing  from   the 


Vertical  Sheathing 
Started.       ? 
FIG.  16. — HORIZONTAL  SHEATHING. 

very  beginning  of  the  excavation  it  would  be  difficult  to  keep 
vertical  sheathing  standing  and  in  line  while  the  trench  is  only 
I  to  3  feet  deep,  and  it  would  greatly  interfere  with  casting 


286  SEWERAGE. 

out  the  excavated  material.  It  will  be  better  in  such  a 
case  to  erect  skeleton  sheathing,  with  only  one  set  of  rangers 
and  braces  and  short  uprights,  behind  the  uprights  placing 
plank  laid  horizontally.  When  this  construction  has  been 
carried  down  5  or  6  feet  vertical  sheathing  can  be  started 
and  continued  as  above.  But  even  then  if  the  vertical 
sheathing  is  more  than  8  feet  long  it  will  be  necessary  to  use 
platforms  or  staging,  unless  a  sheathing-plank  can  be  omitted 
every  5  or  6  feet  and  the  earth  cast  out  through  the  open- 
ing thus  left.  On  account  of  the  difficulties  just  described  it 
is  better,  if  the  trench  is  so  deep  as  to  require  more  than 
one  course  of  sheathing,  to  place  shorter  sheathing  in  the  top 
course — for  instance,  6-foot  sheathing  and  then  12-foot  in  a 
15-  to  1 8-foot  trench. 

Some  contractors  use  horizontal  sheathing  altogether,  the 
verticals  being  only  3  or  4  feet  long,  several  being  placed  one 
above  the  other.  Most  American  contractors,  however, 
prefer  the  vertical  sheathing. 

The  size  of  the  rangers  may  vary  between  wide  limits,  but 
in  any  one  trench  they  should  all  be  the  same  length,  and 
when  in  position  the  ends  of  all  should  come  opposite  or 
under  each  other.  Two-inch  plank  may  be  used  for  rangers  in 
ordinary  loamy  or  clayey  soil  and  shallow  trenches,  and  the 
braces  placed  with  sufficient  frequency  to  prevent  their  belly- 
ing too  much.  This  would  in  many  cases  bring  the  braces  so 
close  to  each  other  as  to  interfere  with  the  work,  and  it  will 
then  be  advisable  to  use  4X4  or  4X6  material.  The 
author  prefers  these  in  any  case,  as  being  stronger,  but  neither 
costing  nor  weighing  more,  than  2-inch  plank.  If  excavating- 
machinery  is  used  the  braces  should  be  at  least  5  or  6  feet 
apart,  and  the  rangers  of  4  X  6  or  6  X  8  timber.  The 
deeper  the  trench  the  heavier  should  be  the  rangers  and 
braces. 

The  braces  should  be  heavier  also   the  wider  the  trench, 


PRACJ'TCAL  SEWER  CONSTRUCTION.  287 

since  they  must  act  as  posts.  They  are  often,  for  conve- 
nience, made  of  the  same  size  of  timber  as  that  used  for 
rangers.  Each  brace  must  be  fitted  to  its  place,  since  the 
width  of  a  trench  usually  varies  at  different  points  within  a 
range  of  several  inches.  For  finding  the  length  of  brace 


FIG.  17. — SLIDING  ROD  FOR  MEASURING  BRACES. 

required  it  is  handier  to  use  a  sliding  rod  than  a  measuring- 
rule.  The  brace  should  be  made  a  little  longer  than  the  dis- 
tance between  rangers,  that  it  may  drive  hard  into  place  and 
fit  there  tightly.  To  make  this  driving  easier  one  edge  of 
one  end  of  the  brace  may  be  slightly  bevelled. 

Instead  of  wooden  braces  extensible  iron  ones  are  coming 
into  general  use,  and  for  narrow  trenches  at  least  are  equally 
as  good  and  much  more  convenient,  since  they  can  be  quickly 
adjusted  to  any  position  and  used  over  and  over  again.  For 
wide  trenches  those  in  the  market  are  hardly  stiff  enough,  but 
are  apt  to  buckle  under  extreme  pressure.  Trussed  beams, 
however,  can  be  obtained  with  extensible  ends,  which  meet 
this  objection.  If  much  bracing  is  to  be  done  the  cost  of 
extensible  braces  can  be  saved  in  the  carpenters'  wages  many 
times  over. 

Much  heavier  sheathing  than  here  described  may  be 
necessary  in  deep  trenches  in  some  soils.  In  stiff  marsh-land 
near  New  York  City,  in  a  trench  26  feet  wide  and  25  feet 
deep,  6-inch  sheathing  was  found  necessary,  with  10  X  10 
rangers  and  8x8  braces  5  feet  apart  horizontally  and 
vertically. 

In  cases  where  the  soil  was  soft  round  piles  have  been 
driven  a  few  feet  apart  along  the  side  lines  of  the  trench  before 
excavation,  and  as  this  proceeded  horizontal  sheathing  was 
inserted  behind  the  piles  and  braces  placed  across  the  trench 
between  them. 


288  SEWERAGE. 

The  rangers  and  braces  can  be  used  over  and  over  again  if 
they  are  not  left  in  the  trench;  the  sheathing,  too,  can 
ordinarily  be  used  several  times;  but  each  time  a  set  is  used 
a  few  plank  will  probably  be  broken,  either  in  driving  or  in 
drawing.  As  stated  in  connection  with  Table  No.  21,  good 
sheathing  can  ordinarily  be  used  two  to  five  times,  taking  an 
average  of  all  used  at  the  outset. 

In  many  instances  it  is  desirable  to  leave  the  sheathing 
in  the  trench,  sometimes  with  and  sometimes  without  the 
rangers  and  braces.  The  conditions  calling  for  leaving  in 
sheathing  are :  that  drawing  it  may  endanger  the  sewer,  or 
water-  or  gas-pipes  in  the  street  near  the  trench,  or  adjacent 
buildings,  or  that  the  street-paving  will  be  injured  thereby. 
The  danger  to  buildings  usually  exists  only  in  connection  with 
deep  trenches  in  unstable  soil  or  where  a  building  is  quite 
near  a  sewer  which  lies  below  its  foundation.  Water-  or  gas- 
mains  would  be  endangered  if  within  two  or  three  feet  of,  and 
more  than  that  distance  above  the  bottom  of,  a  sewer-trench 
in  fairly  good  soil.  If  the  soil  has  shown  a  tendency  to  crack 
along  the  banks  near  the  trench  the  sheathing  should  not  be 
drawn  if  the  street  is  well  paved ;  and  if  water-  or  gas-pipe  or 
other  sewers  are  laid  in  such  street  the  judgment  of  the 
engineer  must  decide  at  what  distance  they  may  be  consid- 
ered safe  from  disturbance  if  the  sheathing  be  drawn.  If  the 
sheathing  has  been  driven  below  the  centre  of  a  sewer,  as 
must  be  done  under  some  conditions,  its  removal  would  dis- 
turb the  foundation  of  the  sewer  and  should  not  be  attempted. 
But  if  two  or  more  courses  of  sheathing  have  been  driven 
all  but  the  lowest  course  may  be  removed  if  the  sewer  only 
is  affected.  The  rangers  and  braces  as  well  as  the  plank  should 
usually  be  left  in.  If  the  banks  are  liable  to  cave  with  the 
drawing  of  the  sheathing  the  trench  should  be  filled  to  a  dis- 
tance above  the  sewer  at  least  equal  to  its  width  before  the  top 
braces  are  knocked  out  or  any  sheathing-plank  is  entirely  drawn. 


PRACTICAL   SEWER    CONSTRUCTION.  289 

Before  drawing  sheathing  the  back-filling,  if  it  is  not  to  be 
rammed,  should  be  carried  to  a  point  at  least  3  feet  above 
the  bottom  of  the  plank.  The  bottom  set  of  braces  and 
rangers  may  then  be  removed.  If  this  gives  less  than  2  feet  of 
back-filling  above  the  top  of  the  sewer  this  amount  should  be 
thrown  in  and  properly  tamped.  When  the  sewer  is  properly 
covered  the  remaining  braces  and  rangers  may  be  removed 
and  the  sheathing  entirely  drawn.  If  the  bank  should  cave 
badly  on  the  removal  of  the  braces  it  might  break  the  sheath- 
ing, and  in  such  a  case  it  may  be  better  to  continue  back- 
filling and  slowly  drawing  the  sheathing,  each  set  of  rangers 
being  removed  only  as  the  back-filling  reaches  them.  If  there 
is  more  than  one  course  of  sheathing  this  plan  should  be  fol- 
lowed in  every  case  with  all  but  the  top  course,  unless  the 
others  are  to  be  left  in  the  trench,  which  may  be  cheaper  in 
some  cases. 

Drawing  the  sheathing  is  often  a  difficult  matter  if  only 
the  hands  or  a  pick  be  used.  A  convenient  plan  is  to  use  a 
sheathing-puller,  made  of  iron  i£  or  2  inches  thick  and  3  or 


FIG.  18. — SHEATHING-PULLER. 

4  inches  wide.  The  ring  on  the  clamp  should  be  so  placed 
that  the  clamp  will  slide  down  the  sheathing  when  not  sup- 
ported, remaining  constantly  horizontal.  After  placing  this 
in  position  on  a  horse  a  simple  pump-handle  motion  with 
the  lever  will  suffice  to  draw  the  plank.  A  chain  to  be 
hooked  tightly  around  a  sheathing-plank  may  be  used  as  a 
substitute  for  the  clamp,  but  is  not  convenient  for  close 


SEWERAGE. 

sheathing,  which  must  be  pried  apart  to  admit  it.  Better 
than  this  sheathing  puller,  where  excavating-machinery  is 
being  used,  is  to  use  the  engine-power  to  draw  the  sheath- 
ing by  fastening  the  clamp  to  a  hoisting-rope. 

Where  a  building  is  so  situated  with  reference  to  the 
sewer-trench  that  its  stability  is  endangered  thereby  the 
greatest  care  should  be  taken  with  the  sheathing  to  prevent 
any  material  behind  it  from  caving  into  or  in  any  way  enter- 
ing the  trench.  To  insure  this  the  sheathing-plank  must 
be  tight  together — in  sand  it  may  be  necessary  to  use  tongued 
and  grooved  plank — and  their  bottoms  should  be  kept  well 
below  the  bottom  of  the  trench.  If  this  is  done  and  the 
bracing  is  strong  and  stiff  there  should  be  little  danger,  unless 
the  material  is  semi-fluid,  when  it  may  be  impossible  to  pre- 
vent a  settlement  of  the  ground  and  buildings,  unless  by 
freezing  the  soil  by  the  Poetsch  process  (an  exceedingly 
expensive  one)  or  some  similar  method. 

If  a  settlement  of  a  portion  of  a  building-foundation  seems 
probable  the  building  should  be  shored  and  jacked  up.  One 
method  of  accomplishing  this  is  to  make  openings  just  above 
the  ground-surface  6  to  10  feet  apart  and  of  a  size  to  permit 
large  beams — 10  X  12,  or  12  X  14  or  18 — to  be  passed  through 
them.  These  beams  are  supported  at  each  -end  by  jacks, 
which  in  turn  rest  upon  blocking  placed  upon  the  ground.  A 
careful  watch  is  kept  of  these  and  at  the  least  sign  of  settle- 
ment of  the  ground  the  jack  above  is  screwed  up  an  amount 
equal  to  this  settlement.  As  a  further  precaution  it  may  be 
advisable  to  shore  up  the  walls  by  a  sufficient  number  of  heavy 
timbers,  whose  lower  ends  are  supported  upon  platforms  or 
grillage,  wedges  being  placed  under  the  foot  of  each  and 
driven  up  when  necessary  to  make  up  any  settlement  of  the 
ground.  The  shores  at  their  upper  ends  bear  against  beams 
bolted  to  the  walls  of  the  building,  or  in  masonry  walls  are 
received  by  openings  about  a  foot  deep  cut  therein.  Shores 


PRACTICAL   SEWER    CONSTRUCTION.  2QI 

alone  are  often  employed  when  the  building  is  not  valuable 
or  the  danger  is  small. 

ART.  73.     LAYING  SEWER-PIPE. 

It  will  save  considerable  trouble  in  the  laying  of  pipe  if 
the  foreman  has  the  trench  dug  exactly  to  line  and  grade  as 
ascertained  by  measuring  and  plumbing  from  a  grade-line 
already  set.  It  is  better  to  have  the  bottom  a  little  too  high 
rather  than  too  low. 

Pipe  sewer  is  usually  laid  up  the  grade,  and  the  pipes  are 
so  manufactured  that  the  specials  must  be  laid  with  their  bell 
ends  pointing  up.  Laying  the  sewer-pipe  in  this  way  is  more 
likely  to  produce  good  joints,  particularly  if  the  grade  is  at 
all  steep,  since  if  laid  down  grade  a  pipe,  after  being  placed1 
in  position  and  before  the  next  is  laid,  tends  to  slide  away 
from  the  one  next  above  it  and  cause  a  break  in  the  inner 
surface  of  the  sewer  and  a  leaky  joint.  It  is  also  much  easier 
to  lay  pipe  with  the  bell  pointing  ahead,  and  the  cement  joint 
is  apt  to  be  firmer.  The  only  reason  advanced  for  laying  pipe 
down  hill  is  that  the  lower  end  of  the  trench  being  ahead  of 
the  pipe,  any  ground-water  will  be  kept  drained  away  from 
the  sewer  construction.  This  is  discussed  in  Art.  78. 

For  lowering  into  the  trench  pipe  which  does  not  weigh 
more  than  100  pounds  a  convenient  method  is  to  use  a  rope 
of  f  to  i£  inch  diameter  with  a  hook  at  one  end.  The  hook 
is  passed  through  the  pipe  from  spigot  to  bell  and  then  back 
over  the  outside  to  the  middle  of  the  pipe  and  caught  on  the 
rope  there,  so  that  the  pipe  when  suspended  will  be  horizon- 
tal. Or  the  hook  may  pass  through  the  pipe  from  bell  to 
spigot  and  be  simply  caught  over  the  end  of  the  latter.  The 
pipe  is  lowered  over  the  edge  of  the  trench  by  one  man  and 
received  at  the  bottom  by  another  if  light,  or  by  two  if 
heavy,  the  hook  being  unfastened  and  pulled  up.  If  the  pipe 
weighs  more  than  100  pounds  two  men  will  be  required  to 


292 


SE  WERA  GE. 


lower  it,  which  they  do  by  each  holding  one  end  of  a  rope 
which  passes  through  it.  For  pipe  heavier  than  200  pounds 
it  is  advisable  to  use  an  ordinary  three-leg  derrick  with  light 
tackle-block.  The  pipe  is  then  suspended  by  a  rope  or  chain, 
with  a  hook  at  one  end  and  a  ring  at  the  other,  passed  through 
the  pipe  and  so  hooked  that  it  may  be  lowered  in  a  horizon- 
tal position.  A  convenient  arrangement  for  holding  the  pipe 
consists  of  a  hook  (Fig.  19),  which  should 
be  at  least  two  thirds  the  length  of  the 
pipe  and  very  strong  at  the  bend.  The 
ring  must  come  beyond  the  centre  of 
gravity  of  the  pipe  to  prevent  its  falling  off 
the  hook.  By  use  of  this  a  pipe  can 
while  suspended  be  entered  into  the  bell 


FIG.  19.— PIPE-LAYING  of  the  one  previously  laid  and  much  heavy 

HOOK.  lifting  by  hand  avoided. 

Another  method  of  entering  heavy  pipe  after  it  is  in  the 
trench  is  sufficiently  explained  by  the  illustration  Fig.   20. 


////.  //////\. 


FIG.  20. — APPLIANCE  FOR  "ENTERING"  HEAVY  PIPE. 
This  is  made  of  wood  or  iron,  with  a  loose  wheel  on  either 
side  of  the  bar  at  the  bottom. 

Before  a  pipe  is  lowered  into  the  trench  a  "  bell-hole" 
should  be  dug  where  its  bell  will  come,  of  such  size  that  when 
the  pipe  is  in  position  the  jointer  can  pass  his  hand  entirely 
under  and  around  the  front  of  the  bell.  It  is  convenient  to 


PRACTICAL    SEWER    CONSTRUCTION.  293 

have  a  stick  exactly  as  long  as  two  or  three  lengths  of  pipe, 
by  which  the  location  of  each  bell-hole  is  measured  from  pipe 
already  laid,  the  bell-holes  being  dug  for  a  few  lengths  in 
advance  of  the  sewer. 

Two  men  should  be  employed  in  laying  sewer-pipe,  one 
straddling  the  pipe  last  laid,  the  other  in  the  trench  just 
ahead  of  it.  The  latter  as  the  pipe  is  lowered  guides  it  into 
place  and  releases  the  hook  on  the  lowering-rope,  if  one  is 
used.  The  former,  holding  one  end  of  a  length  of  packing  in 
«ach  hand,  places  the  loop  thus  formed  under  and  around  the 
pipe  about  an  inch  from  the  spigot  end  and  guides  this  into 
the  bell  of  the  pipe  last  laid,  taking  care  that  the  packing  also 
enters  the  bell.  With  a  yarning-iron  he  then  pushes  the 
packing  up  against  the  shoulder  of  the  bell  all  around,  being 
first  sure  that  the  pipe  is  "  home  "  in  the  bell.  The  other 
pipe-layer  meantime  supports  the  pipe  at  the  bell  end  and 
shoves  it  home.  The  grade-rod  and  plumb-bob  are  then 
used.  If  the  bell  end  is  too  high  (the  spigot  end  should  be 
all  right,  since  the  previous  pipe  is)  it  may,  if  the  soil  is 
loam  or  loose  clay  or  sand,  be  forced  down  a  quarter  of  an 
inch,  more  or  less,  by  standing  and  jumping  upon  the  top  of 
the  pipe.  (The  pipe-layer  should  never  rest  his  foot  inside 
the  pipe  to  force  it  down,  as  this  is  likely  to  break  the  bell  or 
even  the  pipe.)  If  the  soil  is  stiff  clay  or  gravel  the  pipe 
should  be  removed  and  the  trench  bottom  lowered  sufficiently 
with  the  shovel.  If  the  pipe  is  too  low  it  should  not  be  raised 
by  placing  a  stone  or  piece  of  wood  under  it,  but  should  be 
removed  and  fine  earth  placed  and  rammed  in  the  bottom  of 
the  trench.  By  means  of  the  plumb-bob  the  pipe  should  be 
centred  exactly  under  the  grade-line.  A  convenient  way  of 
doing  this  is  to  suspend  the  bob  from  the  cord  at  a  grade- 
plank,  being  careful  not  to  lower  the  cord  by  its  weight; 
then,  when  the  eye  is  so  placed  that  the  cord  and  plumb-bob 
string  coincide,  the  former  is  projected  by  the  eye  vertically 


294  SEWERAGE. 

into  the  trench  and  should  cut  the  centre  of  the  pipe.  With 
a  circular  salt-glazed  pipe  the  centre  is  known  by  a  streak  of 
light  reflected  from  the  sky,  and  this  streak  should  be  bisected 
by  the  vertical  projection  of  the  grade-cord.  Another  plan 
for  obtaining  a  vertical  projection  of  the  grade-cord  is  to 
stretch  another  cord  a  foot  or  two  vertically  below  it.  But 
this  method  is  less  accurate  in  practice  than  the  other  and  is 
not  recommended.  The  grade-cord  cannot  be  stretched  so 
tight  that  it  will  not  sag  TV  to  J  of  an  inch  at  the  centre,  but 
allowance  may  be  made  for  this  in  using  the  grade-rod.  The 
foreman  or  inspector  who  uses  the  grade-rod  will  need  to  have 
a  short  movable  plank  spanning  the  trench  just  ahead  of  the 
pipe  being  laid,  on  which  to  stand. 

As  soon  as  a  pipe  is  in  position  sufficient  earth  should  be 
placed  and  rammed  on  each  side  of  it  just  back  of  the  bell  to 
prevent  its  moving.  The  next  pipe  is  then  lowered  and  set,, 
and  so  on. 

At  least  two  joints  behind  the  pipe  which  is  being  set  is 
another  man,  who  cements  the  joints.  The  cement  he  usually 
keeps  in  an  iron  pail  of  ordinary  size  (although  one  having 
the  shape  of  a  pan  would  be  better),  just  enough  being  mixed 
at  a  time  to  permit  his  using  it  all  before  it  stiffens.  If  there 
is  any  delay  in  laying  the  pipe  the  pail  should  be  cleaned  out 
lest  the  cement  set  in  it.  The  jointer  should  wear  rubber 
mittens,  and  a  small  trowel  will,  be  found  more  convenient 
than  the  fingers  for  getting  the  cement  out  of  the  pail.  The 
cement  mortar  should  ordinarily  be  about  as  stiff  as  putty, 
but  if  the  trench  is  wet  it  should  be  as  dry  as  it  can  be  and 
have  any  cohesion.  The  jointer  takes  a  handful  of  mortar  in 
each  hand  and  presses  it  into  the  bell  all  around,  drawing  his 
hands  meantime  around  the  joint.  With  a  wooden  or  iron 
calking-tool  he  compacts  the  cement  in  the  joint,  adding 
more  as  is  necessary,  and  with  additional  mortar  he  makes  a 
neat  bevel  outside  the  bell,  continually  pressing  the  mortar 


PRACTICAL   SEWER    CONSTRUCTION. 

firmly  towards  the  bell.  This  bevel  should  not  be  flatter  than 
45°,  since  if  too  much  mortar  be  outside  the  bell  its  weight 
may  cause  it  to  fall  away  from  the  pipe  and  perhaps  draw 
with  it  the  mortar  from  inside  the  bell.  The  compacting  of 
the  cement  is  frequently  omitted,  but  is  necessary  if  tight 
joints  are  to  be  obtained. 

Just  behind  the  jointer  should  be  another  man,  who,  as 
soon  as  a  joint  is  made,  fills  the  bell-hole  carefully  with  fine 
•earth  well  tamped,  and  then  fills  and  tamps  the  same  material 
under  and  around  the  rest  of  the  pipe  up  to  at  least  its 
middle.  His  tamping-bar  should  be  of  wood,  there  being 
danger  of  breaking  the  pipe  if  the  ordinary  iron  ones  are  used, 
and  with  a  face  about  2X4  inches.  If  the  trench  is  wet  so 
that  water  collects  in  the  bell-holes  the  mortar  is  likely  to 
become  softened  and  fall  out  of  the  joint.  To  prevent  this  a 
piece  of  cheese-cloth  may  be  wrapped  tightly  around  the  joint 
after  it  is  made,  as  specified  for  sub-drains;  or  the  bell-hole 
may  be  immediately  filled  with  concrete  thoroughly  com- 
pacted. The  latter  is  the  better  but  more  expensive  plan. 
Where  there  is  much  water  in  the  trench  it  is  strongly  recom- 
mended that  concrete  be  placed  not  only  in  the  bell-holes  but 
entirely  around  the  pipe  at  the  joints  (see  Art.  46). 

In  making  the  joint  it  is  quite  probable  that  some  cement 
will  be  squeezed  into  the  pipe,  forming  a  ridge  or  lumps  on 
the  inside.  To  remove  these  a  bag  or  disk  should  be  drawn 
through  the  pipe  past  the  joint  as  soon  as  it  is  finished,  which 
is  done  by  the  pipe-layers.  The  bag  may  be  an  ordinary 
cement  or  similar  sack,  somewhat  larger  than 
the  sewer,  filled  with  straw  or  excelsior  and  a 
rope  tied  around  its  mouth  and  carried  through 
the  sewer,  being  passed  through  each  pipe  as 
it  is  laid.  The  bag  should  fit  snugly  against  FlG-  21.— PIPE- 

.,  .  „  T  CLEANING    DISK. 

the   pipe   all  around.       Instead  of  the  bag  a 

disk  of  heavy  rubber  packing   bolted   between   two    smaller 


296  SEWERAGE. 

wooden  disks  and  fastened  to  an  iron  rod  may  be  used,  being^ 
drawn  forward  as  in  the  case  of  the  bag.  The  rubber  disk 
should  be  slightly  larger  than  the  sewer. 

When  a  manhole  or  other  break  in  the  sewer  is  reached  in 
the  pipe-laying  the  last  pipe  before  reaching  and  the  first 
after  leaving  it  should  be  omitted  or  left  with  uncemented 
joint,  to  be  laid  while  the  manhole  or  other  appurtenance  is 
being  built.  This  is  on  account  of  the  probability  of  such 
pipe  being  disturbed  or  broken  during  the  construction  of  the 
masonry  before  it  has  been  walled  in.  In  this  or  any  case 
where  a  stretch  of  pipe  ends,  or  when  the  laying  is  temporarily 
stopped,  a  plug  should  be  inserted  in  the  end  of  the  last  pipe, 
and  a  bar  or  stake  driven  against  it  into  the  ground  or  nailed 
to  the  sheathing  to  hold  it  in  position.  The  last  joint  should 
be  left  uncemented  until  laying  is  renewed. 

In  setting  branch  specials  the  earth  where  the  special  will- 
come  should  be  so  excavated  as  to  permit  the  branch  to  rest 
upon  it  firmly  when  in  the  desired  position.  If  necessary 
earth  should  be  placed  and  tamped  under  the  branch  for  this 
purpose.  The  inspector  must  not  forget  to  examine  each 
branch  to  see  that  a  cover  is  cemented  in  it,  unless  the  house- 
connection  is  to  be  built  at  once,  and  also  to  mark  its  location. 
In  wet  soil  particularly  uncovered  branches  may  give  rise  to 
serious  difficulty,  and  an  unlocated  branch  is  worse  than  none 
at  all. 

If  work  must  be  done  in  the  winter-time  great  care  should 
be  taken  to  prevent  the  mortar  from  freezing  and  to  keep  ice 
and 'frozen  dirt  out  of  the  joints.  In  pipe-joints  this  is  not 
very  difficult  if  the  trenches  are  at  all  deep,  since  in  these  the 
temperature  seldom  falls  below  40°.  But  the  sand  for  mortar 
should  be  heated,  and  the  pipe  also,  to  insure  the  removal  of 
all  frost  from  the  bells  and  spigots.  In  shallow  trenches  the 
joints  should  be  covered  as  soon  as  possible  with  at  least  two 
feet  of  unfrozen  earth.  Care  should  be  taken,  particularly 


PRACTICAL   SEWER    CONSTRUCTION.  29? 

when  back-filling  is  dumped  from  excavator-buckets,  that  no 
frozen  lumps  fall  upon  the  sewer. 

The  back-filling  of  trenches  has  been  sufficiently  discussed 
in  Art.  54.  When  this  is  thrown  in  without  ramming  particu- 
lar care  should  be  taken  that  all  pipe  be  first  well  covered  with 
earth,  since  stones  and  frozen  lumps  invariably  roll  to  the  foot 
of  the  face-slope  of  the  back-filling  and  might  crack  unpro- 
tected pipe. 

It  is  frequently  necessary  to  cut  a  sewer-pipe  to  a  certain 
length  or  to  split  one  in  two  to  obtain  a  channel  for  a  man- 
hole bottom.  This  can  be  done  with  a  cold-chisel  and 
hammer,  a  light  cut  being  made  first  entirely  around  or  along 
the  pipe  and  this  gradually  deepened  until  the  pipe  of  itself 
breaks  in  two.  The  pipe  is  sometimes  filled  with  sand  well 
packed  before  the  cutting  is  begun,  but  this  is  not  necessary 
if  care  be  used. 

ART.  74.     BUILDING  MASONRY  SEWERS. 

Circular  or  egg-shaped  masonry  sewers  may  consist  of  a 
ring  of  masonry  of  uniform  thickness  throughout,  or  this  ring 
may  be  much  thicker  in  the  arch  than  in  the  invert,  or  there 
may  be  invert-backing  masonry  resting  upon  a  platform  foun- 
dation or  filling  the  irregular  spaces  of  a  rock  cut.  If  the 
sewer  comes  under  either  of  the  first  two  cases  it  is  usually 
made  entirely  of  either  brick  or  concrete,  owing  to  the 
expense  of  dressing  stone  to  make  tight  work  in  compara- 
tively thin  rings  and  to  give  a  smooth  interior  surface.  For 
massive  masonry,  as  in  invert-backing  or  heavy  arches,  stone 
can  be  used  and  is  in  many  cases  cheaper  than  brick.  In  some 
instances  concrete  may  be  cheaper  and  better  than  either. 

A  simple  ring  invert  can  be  used  only  where  the  soil  is 
firm  and  compact  enough  to  stand  when  given  the  shape  of 
the  outside  of  the  invert;  such  as  clay,  pure  or  mixed  with 
sand  or  loam.  If  it  will  not  retain  this  shape  while  the  sewer 


SEWEXAGE. 


is  being  built,  but  is  solid  enough  to  offer  good  foundation, 
as  damp  sand,  the  bottom  of  the  trench  may  be  given  a  flatter 
curve  and  lined  with  a  board  or  plank  cradle,  upon  which 
concrete  or  stone  masonry  is  placed  for  the  invert-backing,  to 
be  lined  with  4  inches  of  brick-work.  In  rock  cuts  the  same 
plan  may  be  adopted,  since  it  is  usually  impracticable  to  bring 
the  rock  to  the  exact  shape  of  the  sewer  (see  Plate  VI,  Fig. 

10). 

If  artificial  foundation  is  necessary  this  usually  consists  of 
a  platform,  upon  which  the  masonry  rests,  and  which  is  placed 
directly  upon  the  trench  bottom  or  supported  upon  piles. 

If  the  arch  is  of  such  dimensions  that  the  thrust  is  more 
than  the  banks  can  be  trusted  to  sustain,  and  a  shape  similar 
to  that  shown  in  Plate  VI,  Fig.  5  or  9,  is  adopted,  concrete 
or  stone  masonry  may  be  used  for  the  side  walls,  and  a  plat- 
form is  generally  necessary  for  foundation  except  in  a  rock 
trench. 

Where  no  invert-backing  is  necessary  the  method  usually 
employed  is  as  follows:  Templets,  two  for  each  gang  of 
masons,  are  provided  conforming  to  both  the  inside  and 
outside  shape  of  the  sewer.  A  convenient  form  is  shown  in 
Fig.  22,  which  is  for  two  rings  of  brick.  This  is  made  of 


m 


B 

FIG.  22. — TEMPLET  FOR  BRICK  SEWERS. 

boards  or  plank,  2-inch  plank  being  sufficiently  heavy  for  any 
but  very  large  sewers.  A  templet  for  an  egg-shaped  sewer 
can  of  course  be  made  in  the  same  way.  Each  ring  of  brick 


PRACTICAL   SEWER    CONSTRUCTION.  299 

is  represented  in  the  templet  by  a  layer  of  plank,  its  inside 
edge  conforming  to  the  inner  surface  of  said  ring.  A  number 
of  fourpenny  or  fivepenny  nails  are  driven  along  the  edge  of 
each  plank  at  equal  intervals,  the  space  between  them  being 
the  thickness  of  a  brick  plus  that  of  the  mortar-joint,  usually 
about  2\  inches.  Each  templet  should  be  an  exact  duplicate 
of  the  other,  including  the  position  of  the  nails.  At  the  exact 
centre  A  of  the  cross-piece  a  notch  is  cut  or  a  nail  driven. 

When  the  bottom  of  the  trench  is  about  to  grade  one  of 
these  templets  is  set  in  a  vertical  position  so  that  the  centre 
of  the  cross-piece  is  exactly  in  the  centre  line  of  the  sewer, 
the  cross-piece  level,  and  the  inside  of  the  templet  at  the 
proper  grade  for  the  sewer-inverU  About  12  to  20  feet  along 
the  trench  the  other  templet  is  similarly  set,  the  sides  of  the 
templets  containing  the  nails  facing  each  other.  If  now  a 
cord  is  stretched  from  any  nail  in  one  templet  to  a  correspond- 
ing nail  in  the  other  the  excavation  should  be  exactly  the 
same  distance  outside  this  as  is  the  outside  of  the  templet. 
If  the  excavation  should  be  carried  too  far  it  must  be  filled 
with  sand  well  rammed,  or  with  good  cement  mortar. 

The  cord  is  now  stretched  between  the  lowest  nails  in  the 
outer  rings  of  the  two  templets,  and  the  brick  laid  to  this  line 
from  end  to  end.  The  cord  is  now  shifted  to  the  next  nail 
in  the  same  ring  and  the  next  row  of  brick  laid.  When  two 
or  three  courses  have  been  laid  on  one  side  of  the  centre  the 
same  number  are  laid  on  the  other  side,  and  both  sides  of  the 
sewer  are  carried  up  simultaneously,  for  which  reason  the 
masons  usually  work  in  gangs  of  2,  4,  6,  or  8.  Not  more 
than  the  last  number  can  work  to  advantage  on  one  section  of 
invert,  but  several  sections  may  be  under  construction  simul- 
taneously. 

When  four  or  five  courses  have  been  laid  a  plank  is  placed 
on  these  for  the  masons  to  stand  on,  and  the  brick-work  is 
continued  row  by  row,  each  row  being  laid  carefully  to  line. 


3oo 


SEWERAGE. 


The  bricks  of  succeeding  courses  should  break  joints  at  least 
3  inches. 

After  the  outer  ring  has  been  completed  to  the  springing- 
line  the  next  is  laid  in  the  same  way.  The  bricks  of  each 
ring  should  be  bedded  in  mortar  at  least  -J  inch  thick,  and 
every  joint  should  be  completely  filled.  Considerable  diffi- 
culty will  be  found  in  getting  any  but  experienced  sewer- 
masons  to  lay  the  brick  radially,  but  smooth  work  cannot  be 
obtained  otherwise  and  this  must  be  insisted  upon.  All 
joints  should  be  carefully  struck.  If  they  are  not  they  should 
be  afterward  raked  out  and  pointed. 

If  the  brick  do  not  absorb  more  than  2  or  3  per  cent  of 
water  in  the  absorption  test  they  should  not  be  wet,  as  they 
cannot  then  be  made  to  stay  in  place.  But  if  they  take  more 
water  than  this  they  should  be  wet  just  before  using.  A 
quick  test  for  this  on  the  ground  is  to  drop  a  brick  into 
mortar  and  remove  it.  If  the  mortar  does  not  in  two  or 
three  minutes  grow  dry  where  it  touches  the  brick  they  prob- 
ably do  not  need  wetting. 

The  mortar  is  usually  mixed  in  a  box  on  the  bank  (it 
should  never  be  mixed  on  the  ground  for  any  purpose)  and 
lowered  into  the  trench  in  a  pail  by  a  rope  provided  with  a 
hook,  where  it  is  emptied  onto  the  mortar-boards.  These 
boards  are  usually  24  to  30  inches  square.  The  brick  is 
placed  in  hods  on  the  bank  and  lowered  to  the 
masons.  A  convenient  form  of  hod  is  shown 
by  Fig.  23,  which  is  made  of  sheet  iron  and 
can  be  quickly  filled  and  emptied.  The  ma- 
terial is  usually  lowered  by  hand  for  small 
sewers,  and  the  man  who  does  this  should 
^_  have  a  heavy  leather  palm-piece  for  each  hand. 

FIG.  23.— HOD  FOR  A  leather  glove  or  mitten  would  not  last  a 
LOWERING  BRICK.  day  of  hard  usage  at  such  work.  To  permit 
of  lowering  the  material  a  platform  is  usually  thrown  across 


PRACTICAL   SEWER    CONSTRUCTION.  3OI 

thj  trench  above  where  the  masons  are  working.  If  stone  is 
being  laid,  or  much  material  is  to  be  used  at  one  place,  or  the 
trench  is  quite  deep,  the  material  may  be  lowered  by  a  wind- 
lass set  in  a  portable  frame  or  by  a  derrick.  If  excavating- 
machinery  is  being  used  this  may  be  utilized  for  lowering  the 
material. 

As  the  invert  of  the  sewer  rises  it  becomes  difficult  for  the 
masons  to  lay  the  brick,  and  the  material  if  in  the  bottom  of 
the  sewer  is  too  far  from  the  work.  A  platform  is  then 
necessary  and  can  be  made  by  sawing  plank  of  such  length  as 
to  be  at  the  desired  elevation  when  placed  horizontally  cross- 
wise of  the  sewer.  Three  or  four  of  these  can  be  thus  laid, 
with  a  few  brick  under  the  centre  of  each  as  additional  support, 


FIG.  24. — MASONS'  PLATFORM  FOR  BRICK  SEWERS. 

and  a  platform  of  loose  plank  placed  over  them.  But  this  is 
apt  to  distort  the  green  brick-work  at  the  ends  of  the  cross- 
plank,  and  it  is  better  to  have  a  number  of  plank  cut  to  the 
shape  of  the  sewer-invert  cross-section,  which  will  distribute 
the  load  along  their  entire  length,  and  to  rest  the  platform 
on  these  (see  Fig.  24). 

When  one  section  of  invert  is  completed  one  of  the 
templets  is  moved  ahead  the  length  of  a  section  and  set.  The 
other  will  not  be  needed  by  the  masons,  since  one  end  of  the 
cord  will  be  fastened  to  nails  stuck  into  the  joints  of  the 
invert  just  completed.  The  second  templet  can,  however,  be 
used  to  advantage  for  grading  the  trench  ahead  of  the  masons. 

In  bonding  the  new  work  with  that  previously  laid  (the 


302  SEWERAGE. 

end  of  which  should  be  toothed  or  racked  back)  all  loose 
brick  and  mortar  should  be  removed,  and  the  brick  cleaned 
and  wetted  before  applying  fresh  mortar. 

The  arch  of  the  sewer  is  built  upon  a  "  centre,"  which  is 
removed  when  the  arch  is  completed  and  the  mortar  suffi- 


FIG.  25. — CENTRE  FOR  BRICK  SEWERS. 

ciently  set.  The  centre  usually  consists  of  lagging  supported 
by  curved  ribs  of  wood  or  iron.  Probably  the  most  common 
form  is  that  shown  in  Fig.  25.  To  templets  similar  in  form 
and  general  construction  to  those  for  the  invert  are  nailed 
lagging-strips  about  I  inch  thick  and  i£  inches  wide,  spaced 
2j  inches  between  centres,  there  being  a  templet  at  each  end 
and  intermediate  ones  spaced  3  or  4  feet  apart.  The  lagging- 
pieces  should  be  perfectly  parallel,  as  their  edges  are  used  for 
lining  the  brick-work.  If  the  radius  of  the  arch  exceeds  2 
or  3  feet  the  lagging  may  be  of  i^-  or  2-inch  by  3^-inch 
strips,  spaced  4^  inches  between  centres;  but  the  2j-inch 
spacing  will  give  a  better  surface  whatever  the  radius.  The 
templets  should  lack  3  or  4  inches  of  being  complete  semi- 
circles, so  that  when  in  position  the  bottom  of  the  centre  may 
be  about  i£  or  2  inches  above  the  springing-line  of  the  arch. 
The  centre  may  be  held  in  position  by  a  triangular  frame 
under  each  templet,  supporting  a  plank  along  each  side  of  the 
sewer,  upon  which  the  centre  rests,  it  being  raised  to  exact 
position  by  wedges,  as  shown  in  Fig.  2$.  When  the  arch  is 


I  PRACTICAL   SEWER    CONSTRUCTION.  303 

completed  the  wedges  are  knocked  out  and  the  centre  drops 
onto  the  two  planks  and  can  be  pulled  forward,  sliding  upon 
these.  It  is  sometimes  difficult,  particularly  with  large  and 
heavy  centres,  to  draw  them  out,  and  to  facilitate  this  a  light 
temporary  track  has  in  some  instances  been  built  under  the 
centre,  which  was  placed  upon  wheels  which  rose  2  or  3 
inches  above  the  track  when  the  centre  was  wedged  up  into 
position.  By  knocking  out  the  wedges  the  centre  drops  onto 
the  track  and  can  be  readily  rolled  forward.  The  use  of  rings 
of  angle-iron  to  support  the  lagging  gave  good  satisfaction  in 
Denver,  Col.  (see  Transactions  of  Am.  Soc.  Civil  Engineers, 
vol.  XXXV,  page  1 13).  For  very  large  sewers  it  may  be  better 
to  build  each  centre  in  place  and  take  it  apart  in  order  to 
move  it. 

The  arch  should  be  built  up  at  a  uniform  rate  on  both 
sides  at  once,  and  the  last  row  of  brick  to  be  laid  in  each  ring 
should  be  at  the  crown  and  should  be  driven  tightly  into  place 
as  a  key.  It  may  be  necessary  to  split  brick  for  this  purpose, 
but  it  is  better  to  have  on  hand  a  number  of  thin  arch-brick 
(of  wedge-shaped  section),  hard  and  tough,  which  will  stand 
driving.  The  outside  of  the  arch  is  usually  plastered  with  £ 
to  £  inch  of  mortar.  The  centre  should  be  left  under  until 
the  mortar  is  so  set  that  there  is  no  danger  of  the  arch 
becoming  deformed  if  it  is  drawn,  the  time  varying  with  the 
character  of  cement,  shape  and  thickness  of  the  arch,  and 
other  details  of  construction.  It  is  probably  well  in  most 
cases  to  back-fill  to  the  crown  of  the  arch  as  soon  as  it  is  com- 
pleted. But  if  the  soil  is  wet,  like  muck,  or  if,  when  excavat- 
ing-machinery  is  used,  the  buckets  usually  contain  consider- 
able water,  no  back-filling  should  be  done  until  the  mortar  is 
thoroughly  set. 

If  the  arch  is  of  stone  or  concrete  masonry  lined  with 
brick  the  brick  ring  is  laid  as  described  above  and  the  stone 
or  concrete  built  on  top  of  it.  The  arch  is  sometimes  built 


304  SEWERAGE. 

of  concrete  without  a  lining,  in  which  case  the  lagging-strips 
must  be  set  close  together.  In  the  Wachusett  (concrete) 
Aqueduct,  1 1  feet  6  inches  in  diameter,  sheets  of  galvanized 
iron  and  zinc  greased  with  black-oil  were  fastened  over  the 
lagging  on  the  centres  with  good  results. 

After  the  removal  of  the  centre  the  arch  masonry  will 
ordinarily  be  found  somewhat  uneven,  with  mortar  adhering 
in  flat  lumps  to  a  large  part  of  its  surface.  These  should  be 
removed  and  the  joints  so  pointed  as  to  render  the  surface 
more  even,  or  the  whole  inside  of  the  arch  may  be  plastered. 

If  there  is  masonry  backing  to  the  invert  this  is  usually 
laid  as  uncoursed  rubble  or  concrete  up  to  within  4^  inches 
of  the  invert-surface,  the  templet  having  been  set  to  indicate 
this,  and  the  brick  lining  is  then  laid  as  above  described.  If 
concrete  is  used  and  is  not  carried  to  the  sides  of  the  trench 
(see  Plate  VI,  Fig.  9)  a  form  of  plank  is  used,  inside  which 
the  concrete  is  rammed,  and  the  plank  removed  when  this  is 
set.  If  the  trench  is  sheathed  and  the  concrete  is  built 
against  the  sheathing  this  cannot  be  pulled,  but  must  be  left 
in  or  cut  off  above  the  concrete.  If  stone  masonry  is  used 
for  invert-backing  it  is  better  to  lay  the  course  of  stone  next 
to  the  brick  lining  with  radial  beds. 

If  concrete  is  used  for  the  entire  sewer  special  forms  must 
be  made  for  each  size  of  sewer,  at  least  two  sets  being  in  use 
by  each  gang.  The  form  for  the  invert  may  be  made  similar 
to  an  arch-centre,  except  that  the  lagging  must  make  tight 
joints  (its  edges  being  bevelled  to  permit  of  this)  and  only  the 
two  or  three  on  the  bottom  be  fastened  to  the  templets. 
This  form  is  fixed  in  position,  concrete  is  placed  in  the 
bottom,  between  the  lagging  and  the  earth,  and  rammed ;  one 
or  two  strips  of  lagging  are  then  slipped  into  position  on  each 
side  and  concrete  placed  and  rammed  behind  these;  more 
strips  are  added  and  concrete  rammed  behind  them,  and  so 
on  until  the  concrete  is  brought  to  the  springing-line  of  the 


PRACTICAL   SEWER    CONSTRUCTION. 


305 


arch.  The  forms  should  not  be  removed  until  the  concrete 
is  set.  There  is  much  danger  that  in  this  invert  construction 
dirt  and  stones  will  get  into  the  concrete,  to  its  detriment, 
and  great  care  must  be  taken  to  avoid  this.  The  forms  must 
be  strongly  braced  down  from  the  bank,  to  resist  their  ten- 
dency to  rise  when  the  concrete  is  rammed.  The  concrete 
should  be  just  wet  enough  to  permit  water  to  be  brought  to 
the  surface  by  light  ramming.  No  heavy  rammers  should  be 
used. 

For  making  a  concrete  arch,  if  there  is  no  brick  lining, 
a  centre  is  used  with  close  lagging,  or  an  open-lagged  centre 
may  be  covered  with  sheet  metal,  as  on  the  Wachusett 


FIG.  26. — FORM  FOR  CONCRETE  ARCH. 

Aqueduct  mentioned  above.  The  outside  form  may  be  con- 
structed as  shown  in  Fig.  26,  the  forms  being  placed  3  to  5 
feet  apart,  the  lagging  being  loose  and  put  in  one  strip  at  a 
time. 

Concrete  sewers  have  been  built  in  a  "  travelling  mould  " 
(Ransome  method),  by  use  of  which  the  entire  sewer  is  con- 
structed continuously,  foot  by  foot.  A  core  in  the  shape  of  a 
ribbon  which  can  be  readily  withdrawn  after  use  (Chenoweth 
system)  has  been  used  for  small  concrete  sewers,  to  which  the 
use  of  the  ordinary  centre  and  form  is  not  adapted. 


306  SEWERAGE. 

Concrete  sewers  are  used  extensively  in  Paris,  Hamburg, 
Brussels,  and  many  other  European  cities.  Quite  a  number 
of  American  cities  have  built  certain  of  their  sewers  of  con- 
crete, among  these  Washington,  D.  C.,  Reading,  Pa.,  and 
Salt  Lake  City. 

ART.  75.     BUILDING  MANHOLES  AND  OTHER 
APPURTENANCES. 

These  can  most  conveniently  be,  and  usually  are,  built  of 
brick.  The  foundation  is  sometimes  of  brick,  but  concrete 
is  better  in  most  cases.  A  stone  slab  set  on  concrete  makes 
a  good  bottom  for  catch-basins. 

The  channel  through  a  pipe-sewer  manhole  is  sometimes 
built  of  brick,  but  a  split  pipe  is  better.  If  brick  be  used, 
the  inside  of  the  channel  should  be  plastered  with  a  coat  of 
neat  Portland  cement.  If  any  branch  channel  in  a  manhole 
is  not  to  be  used  at  once  it  should  be  temporarily  closed  to 
prevent  deposits  forming  in  it.  The  bench  may  be  built  up 
of  brick  plastered  on  top  with  cement,  or  of  concrete.  Or 
the  whole  manhole  bottom  may  be  of -concrete,  a  wooden  core 
being  slipped  into  the  opposite  pipes  and  spanning  the  man- 
hole to  give  the  shape  to  the  channel. 

In  leaving  the  manhole-opening  in  a  brick  sewer  the  end 
brick  in  every  alternate  course  of  the  outside  ring  may  be 
laid  radially,  thus  presenting  toothing  protruding  at  right 
angles  to  the  sewer-barrel.  In  this  steps  with  horizontal 
treads  can  be  built  of  brick  trimmed  to  the  necessary  shape, 
from  which  the  manhole  can  be  carried  up  without  danger  of 
its  sliding  off  the  sewer. 

To  insure  having  the  manhole  of  the  proper  size  and  shape 
a  board  templet  may  be  used,  being  laid,  in  pipe-sewer  man- 
holes, upon  the  concrete  foundation  when  this  has  set,  and 
the  brick  started  by  it  and  carried  vertically  to  the  proper 


PRACTICAL   SEWER    CONSTRUCTION.  3^7 

height.  Another  templet  24  inches  diameter  is  fastened  at 
the  level  of  the  top  of  the  brick-work,  its  centre  vertically 
above  that  of  the  bottom  templet.  Cords  are  strung  from 
the  edge  of  the  top  templet  to  the  top  of  the  vertical  part  of 
the  brick  wall,  spaced  about  2  feet  apart  around  its  circum- 
ference, and  the  brick  laid  to  these.  An  experienced  man- 
hole mason,  however,  can  build  almost  as  symmetrical  a 
manhole  by  eye  only,  and  more  quickly  than  if  strings  are 
used. 

When  the  wall  is  about  2  or  3  feet  high  the  benches  and 
channels  of  the  bottom  may  be  constructed.  It  is  well  to  lay 
plank  in  the  bottom  over  the  channels  temporarily,  to  keep 
mortar  and  dirt  out  of  them  and  out  of  the  sewer  during  con- 
struction, as  well  as  to  hold  the  brick  and  mortar  being  used. 
The  first  step  should  be  placed  about  1 8  inches  or  2  feet  above 
the  bench.  When  the  wall  is  about  4  feet  high  four  piles  of 
brick,  each  8  inches  square  and  about  3  feet  high,  may  be 
made  on  the  bottom  of  the  manhole  and  a  platform  of  short 
loose  plank  be  placed  on  these,  entirely  filling  the  manhole. 
This  holds  the  mason,  brick,  and  mortar  until  another  3  feet 
are  built,  when  a  second  platform  is  similarly  placed  3  feet 
higher.  These  are  of  course  removed  when  the  brick-work  is 
completed. 

The  brick  in  a  manhole  may  be  laid  as  all  headers,  all 
stretchers,  all  on  end  with  their  edges  exposed,  or  a  combina- 
tion of  any  two  or  all  of  these.  Bats  may  be  used  in  large  or 
small  proportion  or  not  at  all.  A  strong  manhole  can  be 
built  by  using  three  courses  of  stretchers  to  one  of  headers, 
all  whole  brick,  until  a  diameter  of  about  3  feet  is  reached, 
and  from  there  to  the  top  using  three  courses  of  squared  bats, 
to  one  of  headers.  The  outside  of  the  manhole  should  be 
plastered  as  the  wall  is  built,  since  it  may  be  impossible  to 
reach  it  afterward.  The  head  should  be  set  as  soon  as  the 
brick-work  is  completed,  and  the  opening  back-filled. 


308  SEWERAGE. 

If  the  manhole  is  shallow,  or  for  any  other  reason  the 
-diameter  is  to  be  rapidly  reduced  towards  the  top,  this  is 
ordinarily  done  by  making  each  ring  of  brick  a  little  smaller 
than  the  one  below,  the  diameter  of  the  manhole  being 
reduced  by  I  to  4  inches  with  each  ring.  Or  it  may  be 
.arched  (Plate  IX,  Fig.  2),  when  the  back-filling  around  it 
.should  be  thoroughly  tamped  to  assist  in  taking  the  thrust. 
In  the  case  of  flush-tanks  particularly  a  flat  iron  ring  is  some- 
times built  in  the  outside  of  the  brick-work  at  the  bottom  of 
the  arch  as  a  precaution. 

Flush-tanks  are  built  in  a  manner  similar  to  the  above. 
These,  except  at  the  very  top,  and  catch-basin  inlets,  are 
usually  larger  in  diameter  than  manholes,  and  are  built 
throughout  of  whole  brick.  Extra  care  should  be  taken  to 
have  all  joints  filled  with  cement  and  tight,  and  the  work  well 
bonded.  After  the  cement  in  flush-tanks  and  catch-basins 
has  fully  set  they  should  be  given  on  the  inside  two  or  three 
washes  of  neat-cement  grout,  laid  on  with  a  whitewash  or 
similar  brush,  care  being  taken  to  cover  the  entire  sur- 
face with  each  coat,  which  should  be  allowed  to  dry  before 
the  next  is  applied.  This  will  seldom  fail  to  give  a  tight 
wall. 

No  water  should  be  turned  into  the  trench  for  flushing  or 
other  purposes  before  the  cement  in  these  appurtenances,  as 
well  as  in  the  sewer,  has  set. 

If  masonry  in  either  sewers  or  their  appurtenances  is  laid 
in  freezing  weather  special  measures  and  precautions  should 
be  taken.  The  sand,  stone,  brick,  and  water  should  all  be 
heated  before  being  used,  and  special  care  taken  to  see  that 
no  ice  or  frozen  dirt  is  in  the  mortar,  on  the  stone  or  brick, 
around  the  sub-drain,  under  the  pipe,  or  under  or  behind  the 
brick  or  concrete  sewer-invert.  To  insure  the  last  it  is  well 
to  take  out  the  last  foot  or  two  of  trench  just  before  the  sewer 
is  to  be  laid  in  it.  If  any  frozen  earth  is  found  under  the 


PRACTICAL    SEWER    CONSTRUCTION.  309 

sewer  grade  it  should  be  removed  and  replaced  by  sand  or 
gravel  thoroughly  rammed. 

The  water  for  mortar  can  be  conveniently  heated  by 
injecting  into  it  steam  (as  the  exhaust  from  a  pump-  or  exca- 
vator-engine), it  being  kept  in  several  hogsheads  or  oil- 
barrels.  The  brick  and  stone  can  be  heated  by  piling  them 
as  in  brick-kilns  and  burning  a  wood  fire  under  them;  and  the 
sand  by  being  piled  over  these,  or  in  large  iron  pans  such  as 
are  used  for  heating  asphalt. 

ART.  76.     FOUNDATIONS. 

Piles  are  ordinarily  used  for  sewer-foundations  in  soft  soil. 
They  usually  support  a  timber  platform,  but  in  some  instances 
concrete  is  placed  directly  upon  and  around  their  heads.  For 
driving  them  the  ordinary  pile-drivers  are  used,  or  they  are 
sunk  by  the  water-jet.  If  they  are  to  support  platform 
timbers  they  must  be  driven  carefully  to  line  and  sawed  off 
accurately  to  grade.  It  will  sometimes  be  advisable  to  drive 
the  piles  before  the  excavation  has  proceeded  very  far,  using 
piles  considerably  longer  than  actually  required,  as  the  jarring 
of  the  banks  of  the  trench  may  thus  be  avoided,  as  well  as  the 
inconvenience  of  moving  the  driver  through  or  over  a  trench 
full  of  braces.  The  objection  to  this  plan,  aside  from  the 
cost  of  the  additional  length  of  the  piles,  is  that  they  interfere 
with  the  excavation. 

In  moving  an  ordinary  pile-driver  through  the  trench  it 
will  be  necessary  to  remove  the  braces  ahead  of  it.  But  no 
brace  should  be  removed  until  another  has  been  inserted 
behind  the  driver-frame  between  the  same  rangers  and  as 
close  to  the  first  as  possible.  This  trouble  might  be  avoided 
in  many  cases  by  placing  the  pile-driver  on  a  track,  on  a  level 
with  the  ground,  over  the  centre  of  the  trench;  or  the  track 
may  be  on  the  surface  at  one  side  of  the  trench.  The  driver 


310  SEWERAGE. 

is  then  provided  with  movable  hammer-guides,  which  can  be 
lowered  into  the  trench  and  raised  with  ease.  The  use  of  the 
steam-hammer  pile-driver  is  often  advantageous,  and  in  sandy 
soils  the  water-jet  can  be  used  to  advantage.  Neither  of 
these  last  is  interfered  with  in  its  operation  by  the  bracing. 

The  dimensions  and  construction  of  the  platform  follow 
the  rules  for  ordinary  foundations.  There  is  usually  but  one 
set  of  timbers  under  the  planking,  which  is  in  most  cases 
composed  of  one  or  two  layers  of  2-inch  to  4-inch  plank,  as 
in  Plate  VI,  Figs.  3,  5,  and  6;  although  in  some  instances 
heavy  timbers  are  used,  as  in  Plate  VII,  Fig.  10.  Any 
timber  which  is  to  be  placed  where  it  will  not  be  continually 
wet  should  be  creosoted. 

If  a  platform  is  used  without  piling,  sills,  longitudinal  or 
cross,  should  be  placed  under  the  planking,  although  in  the 
case  of  small  sewers  these  may  consist  of  lengths  of  2-inch 
plank  only.  Platforms  without  piling  or  heavy  sills  are  of 
little  permanent  service  under  large  sewers,  but  during  con- 
struction may  serve  to  prevent  local  distortion  of  the  masonry 
before  the  cement  has  set.  One  or  two  lines  of  plank  placed 
lengthwise  under  a  pipe  sewer,  however,  are  in  many  cases  of 
permanent  value,  back-filling  being  thoroughly  filled  and 
rammed  between  the  pipe  and  the  plank. 

Among  the  best  of  our  woods  for  foundations  are  the 
cedar,  oak,  elm,  alder,  and  beech.  All  bark  should  be 
removed  and  the  sap  dried  out  from  piling  or  sawed  timber. 
The  platform  timbers  should  be  fastened  to  the  piles  with 
iron  drift-bolts  or  treenails.  . 

ART.  77.     PUMPING  AND  DRAINING. 

Next  to  quicksand,  water  is  probably  the  worst  enemy  of 
the  sewer-contractor  and  requires  a  large  share  of  the  atten- 
tion of  the  engineer.  If  there  is  but  a  small  trickle  or  ooze 


PRACTICAL   SEWER    CONSTRUCTION.  31 1 

of  water  into  the  trench  it  may  interfere  but  little  with  the 
excavating,  and  will  collect  at  points  in  the  bottomed  trench 
whence  it  can  be  removed  at  intervals  by  a  bucket.  If  the 
amount  becomes  somewhat  greater  it  may  still  be  handled 
without  the  use  of  sub-drains,  that  from  where  the  pipe  has 
been  laid  being  shut  off  by  the  back-filling. 

The  amount  from  the  trench  ahead  of  the  sewer  may  need 
to  be  pumped,  however.  For  removing  small  quantities  of 
water  from  a  trench  probably  nothing  is  better  than  a 
diaphragm-pump.  Tin  "boat-pumps"  are  often  used,  but 
will  not  handle  so  much  water,  are  less  economical  of  power, 
and  are  not  so  convenient  as  the  diaphragm-pump ;  they  can, 
however,  be  used  in  trenches  more  than  20  feet  deep,  where 
the  diaphragm  is  hardly  practicable.  Under  favorable  condi- 
tions a  diaphragm-pump  can  be  made  to  raise  5000  or  6000 
gallons  per  hour.  Diaphragm-pumps  can  be  used  in  deep 
trenches  by  placing  a  second  pump  upon  a  platform  half-way 
down  the  trench,  which  discharges  the  water  into  a.  tub,  from 
which  the  first  pump  raises  it  to  the  surface.  Or  the  upper 
pump  may  not  be  used,  but  a  trough  may  carry  the  discharge 
from  the  lower  one  to  an  opening  in  the  sewer  at  a  point 
where  the  cement  is  so  set  as  to  be  uninjured  thereby,  the 
water  flowing  through  the  sewer  to  its  outlet. 

A  sump-hole  of  ample  size  should  be  made  in  the  bottom 
of  the  trench  to  receive  the  suction-pipe,  which  should  be 
provided  with  a  strainer  at  the  bottom.  If  the  material  is 
sand  or  soft  ground  it  is  well  to  place  a  pail  or  keg  in  the 
sump  to  keep  the  end  of  the  suction-pipe  from  being  buried, 
the  top  of  the  pail  being  just  below  the  level  of  the  trench 
bottom.  The  pail  should  be  watched  and  material  kept  from 
running  over  its  edge.  The  excavation  should  usually  be  so 
carried  on  that  the  whole  trench  slopes  toward  the  sump-hole, 
each  laborer  seeing  that  the  water  flows  through  his  section 
to  the  next  lower. 


312  SEWERAGE. 

Where  a  sub-drain  is  being  laid  the  water  is  frequently 
permitted  to  flow  from  the  trench  under  excavation  to  and 
through  this.  In  many  if  not  most  soils  this  is  bad  policy, 
since  it  leads  to  a  silting  up  of  the  drain  by  the  large  amount 
of  material  washed  in  from  the  trench.  It  is  better  in  most 
cases  to  leave  or  make  a  dam  at  the  upper  end  of  the  com- 
pleted trench,  and  place  a  sump-hole  just  ahead  of  this  and 
below  grade,  from  which  the  water  is  pumped.  When  a  sec- 
tion of  20  or  30  feet  has  been  excavated  to  grade  another 
dam  and  sump-hole  can  be  placed  at  the  head  of  this  section 
and  the  others  removed,  the  sump-hole  being  filled  with  sand 
or  gravel  or  other  good  material  well  rammed. 

Where  a  sub-drain  is  started  from  a  sump-hole,  or  that 
lower  down  the  line  is  found  to  be  too  small  to  carry  the 
water  coming  to  it,  a  pump  must  be  placed  at  this  point  also 
to  remove  the  water  from  the  sub-drain  which  is  to  be  laid 
beyond  it.  This  water  is  frequently  raised  to  the  sewer  only, 
the  pump, being  placed  in  a  manhole  and  discharging  the  water 
below  a  temporary  dam  in  the  sewer,  which  prevents  its  flow- 
ing up  the  sewer  onto  the  work. 

Two  or  more  hand-pumps  are  sometimes  concentrated  at 
one  point  when  the  amount  of  water  is  considerable.  It 
would  in  many  instances  be  cheaper  to  use  a  steam-pump  at 
such  a  place.  Piston,  centrifugal,  and  wrecking  pumps, 
pulsometers,  and  steam-siphons  are  the  steam  appliances  in 
most  common  use  on  sewer  construction.  In  all  of  these  iron 
suction-pipes  are  used,  from  4  to  8  or  10  inches  in  diameter. 
The  piston-pump  is  the  most  economical,  and  adapted  to 
widely  and  rapidly  varying  quantities  of  water,  and  if  the 
water  is  fairly  clean  needs  very  little  attention.  It  cannot, 
however,  pump  gritty  water  without  rapid  deterioration.  The 
centrifugal  pump  can  raise  muddy  or  gritty  water,  chips,  and 
even  small  stones,  its  first  cost  is  less  than  that  of  a  piston- 
pump,  and  it  can  be  repaired  more  cheaply  if  damaged.  It 


PRACTICAL   SEWER    CONSTRUCTION.  313 

requires  a  fairly  constant  and  fixed  quantity  of  water  to  keep 
it  working,  and  is  apt,  especially  when  a  little  worn,  to  give 
trouble  by  losing  its  priming,  when  the  rising  of  water  in  the 
trench  before  it  can  again  be  primed  may  give  trouble.  The 
wrecking-pump  the  author  has  found  to  be  an  excellent  pump 
for  sewerage-work.  It  will  lift  and  discharge  anything  which 
can  pass  through  its  suction-pipe  and  is  extremely  simple  in 
action.  All  these  pumps  must  be  firmly  set  over  or  near  the 
trench  and  their  position  can  be  changed  only  with  consider- 
able labor.  It  is  better  to  set  them  directly  over  the  sump 
and  have  a  suction-pipe  as  short  and  with  as  few  joints  as 
possible. 

The  pulsometer  pumps  muddy  and  gritty  water,  but  is 
not  economical  of  steam  and,  except  in  experienced  hands, 
is  apt  to  act  in  a  provokingly  contrary  manner,  particularly 
after  some  use.  It  has  the  great  advantage,  however,  of 
portability,  being  suspended  by  a  chain,  which  permits  rapid 
changing  of  its  position  without  cessation  of  pumping,  the 
steam  being  conveyed  to  it  through  a  rubber  steam-hose. 
For  pumping  large  quantities  of  water  at  the  point  where 
excavation  is  proceeding  and  where  frequent  change  of  location 
of  pump  and  suction  is  necessary  it  is  perhaps  the  best  contri- 
vance on  the  market.  The  steam-siphon  is  likewise  conve- 
niently portable,  but  is  most  extravagant  of  steam  and  is 
hardly  practicable  for  raising  large  quantities  of  water. 

The  pulsometer  and  siphon  are  particularly  adapted  to 
raising  water  from  the  point  where  the  work  is  progressing 
with  the  least  interference  therewith.  Piston,  centrifugal, 
and  wrecking  pumps  are  best  used  at  a  distance  from  the  work 
to  lift  water  which  has  flowed  to  them  through  sub-drains  or 
the  sewer,  although  they  are  often  used  at  the  work  when  the 
same  sump  can  be  used  for  two  or  three  days  at  a  time. 

All  suction-pipe  on  either  steam-  or  hand-pumps  should  be 
provided  with  a  strainer  at  the  bottom,  and  the  centrifugal 


314  SEWERAGE. 

requires  a  foot-valve,  which  it  is  also  well  to  supply  for  the 
other  steam-pumps.  If  a  chip  or  other  obstacle  should  hold 
this  valve  open  and  prevent  priming  the  suction  a  shovelful 
of  stable  manure  dropped  into  the  suction-pipe  will  in  many 
cases  enable  the  valve  to  hold  its  priming. 

All  parts  of  the  machinery  should  be  readily  accessible, 
particularly  any  valves,  and  wrenches  and  screw-drivers,  pack- 
ing, oil,  waste,  duplicate  nuts,  washers,  etc.,  should  be  kept 
constantly  at  hand.  A  cessation  of  pumping  for  15  minutes 
may  permit  the  water  to  drive  the  workmen  from  the  trench, 
to  soften  the  banks  and  endanger  the  sheathing,  ruin  the 
green  masonry,  stop  up  sub-drains,  or  do  other  serious 
damage.  A  good,  intelligent,  careful  stationary  engineer  is 
a  necessity  on  such  work. 

The  water  raised  from  the  trench  should  not  be  discharged 
upon  the  ground  near  the  sewer,  unless  the  street  has  imper- 
vious pavement,  as  it  might  soak  back  into  the  trench  and  be 
pumped  over  and  over  again.  It  may  be  carried  to  the 
nearest  watercourse  or  sewer-inlet  or  manhole  along  the 
gutters,  in  wooden  troughs,  or  in  sewer-pipe  temporarily  laid 
on  the  ground  with  joints  tightly  calked  with  oakum  or  clay. 

It  usually  pays  to  keep  the  water  pumped  down  all  night, 
«ven  if  there  is  no  work  to  be  damaged  by  its  rising,  as  this 
would  again  fill  the  surrounding  ground  with  water,  which 
might  not  drain  out  for  several  hours  after  pumping  began  the 
next  day.  It  may  be  well  to  whitewash  one  or  two  sheath- 
Ing-plank  down  to  the  trench  bottom  each  evening,  which 
will  give  evidence  next  day  if  the  engineer  has  not  kept  the 
water  down.  A  shelter  should  be  built  in  front  of  the  boiler 
to  protect  the  engineer  from  storms. 

While  using  a  diaphragm-pump  always  have  spare  dia- 
phragms and  an  extra  length  of  suction-hose  on  hand. 

Moving  a  pump  and  boiler  often  costs  more  indirectly  in 
interference  with  the  work  than  the  immediate  expense  comes 


PRACTICAL   SEWER    CONSTRUCTION.  31$ 

to.  In  general  every  effort  should  be  made  to  set  the  pump 
in  such  a  place  and  manner  that  it  need  not  soon  be  moved. 
Be  sure  to  have  the  blocking  under  it  solid,  to  prevent  the 
suction-pipe  joints  from  working  loose  or  breaking. 

ART.  78.     HANDLING  WET  AND   QUICKSAND  TRENCHES. 

if  excavation  is  in  good  material  and  of  comparatively 
uniform  depth  a  sewer  gang  once  organized  should  move  along 
at  a  uniform  rate  of  300  or  400  feet  a  day  for  small  pipe 
sewers,  25  to  200  feet  for  brick  ones,  and  with  little  but 
routine  work  for  the  foreman.  If  genuine  quicksand  is  en- 
countered, however,  every  foot  of  progress  must  be  fought 
for  with  unflagging  energy,  pluck,  and  intelligence.  In 
ordinary  wet  trenches  the  difficulty,  while  not  usually  so 
great,  is  sometimes  considerable.  In  both  an  intelligent 
adapting  of  the  work  to  every  new  exigency  is  necessary. 

Water  is  met  with  as  springs  in  the  trench  or  as  a  general 
exuding  from  all  the  ground.  The  former  can  easily  be 
managed  by  catching  the  water  at  its  point  of  exit  and  pump- 
ing it  away.  If  it  enters  from  the  bottom  of  the  trench  it  can 
sometimes  be  caught  in  a  trough  and  led  back  and  discharged 
into  either  the  completed  sewer  or  into  a  tub  in  which  the 
suction-pipe  of  a  pump  is  placed.  It  is  absolutely  useless  to 
attempt  to  stop  the  water  from  coming  out  of  the  ground; 
the  endeavor  must  be  to  handle  it  after  it  gets  out.  In  the 
case  of  a  spring  in  a  brick-sewer  trench  a  method  often  advan- 
tageous is  to  build  into  the  brick-work  opposite  the  spring  a 
small  pipe,  2  to  4  inches  diameter,  through  which  the  water 
can  enter  the  sewer,  and  to  conduct  it  back  from  there  to  the 
finished  sewer  in  a  trough.  This  pipe  can  be  plugged  after 
the  masonry  is  thoroughly  set,  but  might  better  be  left  open 
to  drain  the  ground  if  in  a  storm-sewer,  or  if  in  a  combined 
sewer  and  well  above  the  line  of  flow  of  house-sewage.  This 


316  SEWERAGE. 

pipe  can,  in  many  cases,  be  so  driven  into  the  bank  at  the 
spring  that  the  water  will  flow  through  it  and  the  trough  be 
set  before  the  brick-work  is  begun  at  that  point,  the  trench 
being  thus  left  dry. 

If  the  water  does  not  enter  as  a  spring  and  consequently 
cannot  be  caught  in  this  way,  but  if  the  ground  is  a  gravel 
or  is  not  readily  softened  by  the  water,  an  outer  ring  of  brick 
may  be  built  with  quick-setting  cement,  and  plenty  of  it  in 
beds  as  well  as  joints,  an  occasional  brick  being  left  out  to 
permit  the  water  to  enter  the  sewer-invert,  over  which  it  can 
flow  to  a  sump-hole  ahead  or  through  the  sewer  below.  If 
openings  are  not  thus  left  in  the  brick-work  the  water  will 
force  its  way  through  the  joints.  Plank  should  be  placed  over 
the  brick-work  as  fast  as  it  is  laid  for  the  masons  to  stand 
upon.  This  outer  ring  when  set  may  be  found  uneven  of 
surface,  but  the  joints  will  probably  be  tight.  The  openings 
may  then  be  closed  by  inserting  a  brick  and  calking  the  joints 
with  cloth,  oakum  and  cement,  wooden  wedges,  tea-lead, 
etc.,  or  a  pipe  may  be  inserted  and  the  water  allowed  to  enter 
it  as  described  above.  The  outer  ring  being  thus  made 
water-tight,  the  inner  ones  can  be  built  as  usual,  any  depression 
in  the  outer  ring  being  well  filled  with  mortar.  In  this  and 
in  all  brick-,  stone-,  and  particularly  concrete-work  which  water 
flows  over  while  green  the  surface  can  be  protected  from  wash 
by  spreading  rather  heavy,  strong  brown  wrapping-paper  over 
it.  Cheap  wood-pulp  paper  is  of  little  use.  The  paper  when 
wet  will  cling  to  the  masonry,  remaining  intact  for  days  and 
even  weeks. 

Another  plan  is  to  dig  a  sump-hole  ij  to  3  feet  deep  in 
the  centre  of  the  section  of  invert  under  construction,  and 
keep  the  water  lowered  in  this  by  a  pump  until  the  brick-work 
is  completed  and  set  everywhere  except  over  the  sump.  If 
the  ground  is  very  porous  the  water  will  all  flow  to  the  sump 
and  leave  the  trench  dry  for  several  feet  in  each  direction. 


PRACTICAL   SEWER   CONSTRUCTION.  3 1/ 

When  the  surrounding  masonry  has  set  the  suction-pipe  is 
removed  from  the  sump-hole,  and  this  is  filled  with  sand, 
gravel,  or  concrete,  thoroughly  rammed.  The  remaining 
brick-work  is  then  laid,  with  or  without  a  pipe  through  it,  as 
described  above. 

A  better  plan  is  to  use  sub-drain  pipe,  discharging  into  a 
sump,  which  is  to  be  pumped  if  there  is  no  outlet  for  it  or  if 
the  drain  below  is  too  small  to  carry  all  the  water.  A  disad- 
vantage in  this  connection  of  building  either  brick  or  pipe 
sewers  down  instead  of  up  grade  is  that  the  water  cannot  be 
run  away  through  the  sewer  or  sub-drain,  whether  it  be 
pumped  or  not,  and  although  it  drains  away  from  the  work  it 
is  only  to  soak  into  the  ground  ahead  and  make  that  all  the 
wetter,  besides  the  fact  that  it  is  accumulated  where  the 
excavation  is  in  progress.  Not  only  this,  but  the  ditch  acts 
as  a  drain  to  conduct  down  to  the  work  water  from  all  the 
territory  above  which  has  been  passed  through,  the  use  of  a 
sub-drain  adding  greatly  to  this  amount.  If  the  trench  be 
dug  up  hill  it  will  while  advancing  tend  to  drain  out  the 
ground  ahead  and  a  trench  may  be  found  dry  which  would  be 
wet  if  approached  from  above.  In  some  instances  where  a 
trench  has  been  extended  up  to  ground  which  seemed  hope- 
lessly wet,  and  the  trench  thoroughly  braced  and  left  open  for 
a  week  or  two,  the  excavation  was  then  resumed  without  diffi- 
culty, the  ground  being  found  comparatively  dry. 

This  fact,  that  wet  ground  will  in  many  cases  drain  out  if 
an  outlet  be  provided,  may  be  taken  advantage  of  in  several 
ways.  For  instance,  if  beneath  the  wet  porous  soil,  but 
above  the  sewer  grade,  is  a  stratum  of  clay  the  trench  may 
be  carried  down  to  this,  braced,  and  allowed  to  drain  out, 
when  the  clay  can  be  readily  cut  out  dry  instead  of  as  a  thick, 
sticky  paste  which  mires  the  feet  and  will  not  leave  the 
shovel.  Quicksand  can  sometimes  be  dried  out  if  the  water 
be  given  an  outlet  and  sufficient  time  allowed.  It  will  then  be 


318  SEWERAGE. 

almost  as  hard  as  rock,  but  much  easier  to  handle  than  in  its 
quick  state. 

If  sewer  construction  is  in  the  shape  of  an  extension  from 
a  line  already  in  use  into  which  the  water  must  not  be  run,  or 
if  it  is  carried  on  in  sections  which  have  no  outlet,  a  pumping- 
station  can  take  the  place  of  an  outlet,  or  a  ditch  can  some- 
times be  carried  to  a  watercourse  lying  below  the  sewer.  The 
latter  is  always  the  better  plan  if  not  too  expensive,  as  there 
is  then  no  danger  from  broken  or  disordered  pumps.  But  the 
ditch  must  be  above  the  reach  of  any  possible  flood  in  the 
stream  into  which  it  discharges. 

A  plan  used  with  success  on  the  Metropolitan  Sewerage 
System  (Boston)  and  elsewhere  is  to  drive  2-  or  2f-inch  pipes 
by  water-jet  on  one  or  both  sides  of  the  trench,  10  to  15  feet 
apart  and  to  a  point  2  or  3  feet  below  the  bottom  of  the 
sewer,  and,  by  connecting  a  number  of  them  to  a  6-inch 
suction-main  and  pumping  on  them  for  a  few  days,  lower  the 
ground-water  before  the  excavation  reaches  this  point,  and 
keep  it  lowered  until  the  work  here  is  completed.  If  the 
trench  is  less  than  about  20  feet  deep  the  pipes  may  be  driven 
outside  the  trench,  but  if  more  it  will  probably  be  necessary 
to  put  them  and  the  pump  inside  the  sheathing  at  a  distance 
of  not  more  than  20  feet  from  the  bottom,  although  they  may 
be  in  the  way  there.  The  sinking  of  such  tubes  in  Newton, 
Mass.,  cost  from  8  to  50  cents  per  foot. 

In  laying  pipe  sewers  in  wet  trenches  much  of  the  above 
is  not  applicable.  The  best  method  for  such  work  is  the  use 
of  sub-drains.  When  the  ground  is  not  excessively  wet  the 
trench  is  then  dry  for  the  laying  of  the  sewer-pipe.  But 
where  there  is  a  large  flow  of  underground  water  it  may  be 
impossible  for  it  to  reach  the  sub-drain,  through  the  overlying 
gravel  or  stone,  as  rapidly  as  it  enters  the  trench.  Frequent 
sumps  must  then  be  provided,  with  a  pump  at  each,  there 
being  always  one  only  a  few  feet  ahead  of  the  sewer.  If 


PRACTICAL   SEWER    CONSTRUCTION. 


319 


water  still  flows  over  the  trench  bottom  to  the  sump  it  may 
be  necessary  to  lay  the  sewer  in  concrete.  In  fact  this  is 
always  desirable,  though  expensive,  in  wet  trenches  or  where 
sub-drains  are  used.  In  using  concrete  it  should  be  placed 
and  rammed  in  the  trench  and 
the  pipe  bedded  in  it  before  it 
sets.  The  concrete  may  be 
brought  up  only  a  short  distance 
above  the  invert  of  the  pipe, 
being  sloped  down  toward  the 
sheathing  and  forming  a  gutter 
on  each  side  in  which  the  water 
may  run  to  the  nearest  manhole 
or  sump.  If  this  flow  is  consid- 
erable plank  or  boards  or  heavy 
paper  may  be  laid  on  the  con- 
crete to  protect  it  from  wash. 
The  rest  of  the  sewer-joint  may 
be  made  in  the  ordinary  way.  It 

is  better,  however,  to  also  carry  the  concrete  entirely  over  the 
sewer  at  the  joints  after  a  stretch  between  manholes  is  com- 
pleted and  the  side  gutters  are  no  longer  needed. 

Water  should  never  be  allowed  to  stand  in  bell-holes  after 
a  pipe  is  cemented.  If  liable  to,  the  bell-hole  should  be  filled 
with  cement  or  concrete,  or  at  least  with  sand  or  gravel  well 
tamped.  No  water  should  be  allowed  to  run  through  a  sewer 
until  the  cement  is  fully  set.  Particular  attention  should  be 
paid  to  branches  and  slants  in  wet  trenches  to  see  that  they 
are  tightly  sealed.  It  is  an  excellent  plan  to  build  a  dam  at 
each  end  of  a  stretch  of  sewer  in  a  wet  trench,  after  the  sewer 
is  completed  and  cement  set,  and  before  back-filling  above 
the  pipe,  and  allow  the  water  to  stand  upon  it  Leaks  thus 
discovered  are  then  readily  accessible  for  repairs. 

In  moderately  wet  ground  it  is  often  advisable  to  place 


FIG.  27. — SEWER-PIPE  LAID  IN 
CONCRETE. 


32O  SEWERAGE. 

dams  across  the  trench  at  intervals  of  15  to  30  feet,  that  there 
may  not  be  so  great  a  stream  continually  flowing  by  the  men 
while  working.  The  head  of  the  trench  being  kept  on  an 
incline,  water  collects  above  each  dam  until  there  are  no  dry 
places  left  in  the  sections  in  which  to  dig,  when  the  dams  are 
opened  in  succession,  beginning  with  the  lowest,  and  the  water 
flows  to  the  sump,  from  which  it  is  pumped.  The  dams  are 
then  closed  and  digging  resumed  immediately  above  each,  the 
laborers  moving  up  the  slope  as  the  water  rises  above  each 
dam. 

The  combination  of  water  with  a  particular  kind  of  sand 
produces  what  is  called  quicksand.  Any  object  resting  upon 
this  sinks  slowly  into  it  until  it  has  displaced  its  own  weight 
of  sand.  But  a  pick  can  hardly  be  driven  into  quicksand 
which  has  not  been  disturbed.  The  sand  is  very  fine  and  is 
easily  stirred  up  and  carried  by  running  water,  but  will 
quickly  settle  into  a  tough,  compact  mass  which,  if  allowed 
to  dry  out,  will  become  almost  as  hard  as  soft  sandstone. 
Quicksand  is  semi-fluid  and  will  run  under  sheathing  unless  it 
be  driven  to  a  considerable  distance  below  the  bottom  of  the 
trench.  If  the  influx  is  not  cut  off  by  deep  sheathing,  by  the 
time  the  excavation  is  2  or  3  feet  into  quicksand  a  point  is 
reached  beyond  which  no  headway  can  be  made,  the  bottom 
remaining  at  the  same  level  however  much  be  taken  out  of  it. 
After  a  time  the  cavities  behind  the  sheathing,  caused  by  the 
flowing  of  the  quicksand  from  there  into  the  trench,  permit 
the  ground-surface  to  settle  or  to  drop  entirely,  and  the 
sheathing,  relieved  of  outside  pressure  and  friction,  is  apt  to 
completely  collapse.  If  there  is  any  possibility  that  such  a 
cavity  is  forming  all  braces  should  be  nailed  to  the  rangers 
and  tied  together  by  cross-bracing,  and  outside  rangers  braced 
against  the  sheathing  from  the  curb  or  other  points  well  back 
of  the  trench.  If  there  is  more  than  one  course  of  sheathing 
the  plank  in  the  upper  ones  should  be  nailed  to  the  rangers. 


PRACTICAL   SEWER   CONSTRUCTION. 


32I 


If  the  ground-surface  should  fall  into  the  cavity  thus  made 
sod,  straw,  brush,  etc.,  should  be  thrown  against  the  sheath- 
ing, which  will  stop  the  quicksand  from  flowing  into  the 
trench.  The  entire  cavity  should  then  be  filled  with  earth, 
ashes,  or  some  good  filling  material.  It  is  in  most  instances 
well,  if  the  condition  is  such  as  is  shown  in  Fig.  28,  to  remove 


Quick 


Sand 


FIG.  28. — SHEATHING  A  BADLY  CAVED  TRENCH. 

a  plank  or  two  here  and  there  from  the  upper  course  of 
sheathing  and  throw  into  the  cavity  sods  or  straw,  and  then, 
after  bracing  the  sheathing  as  above  described,  to  break  down 
the  top  soil  and  fill  the  cavity  with  good  earth.  Fig.  28  is 
no  exaggeration  of  conditions  sometimes  occurring  in  quick- 
sand. A  preventative,  which  is  usually  effective,  is  to  keep 
several  men  continually  driving  the  sheathing  with  light 
mauls,  or  better  still  keep  steam-hammer  pile-drivers  at  work, 
so  that  the  bottom  of  the  sheathing  is  continually  maintained 
a  foot  or  two  below  the  bottom  of  the  trench.  This  is  a  pre- 
caution which  should  never  be  neglected. 

One  effect  of  the  formation  of  the  cavities  described  is 
that  the  top  earth  tends  more  than   ever  to  fall  towards  the 


322  SEWERAGE. 

trench,  and  consequently  the  strain  on  rangers  and  braces 
becomes  severe.  It  is  better  to  multiply  the  number  of 
rangers  than  that  of  the  braces  to  each  ranger,  as  the  trench 
is  then  less  obstructed  for  lowering  materials. 

Quicksand  has  usually  only  a  little  water  flowing  through 
it,  but  that  little  should  be  handled  by  pump  if  possible  and 
not  allowed  to  run  into  the  sewer  or  sub-drain,  the  result  of 
which  would  be  the  rapid  choking  of  the  drain,  or  of  the 
sewer  if  small,  by  quicksand.  Quicksand  should  not  be 
thrown  directly  back  upon  the  finished  sewer,  as  its  angle  of 
stability  is  exceedingly  small,  and  it  is  apt  to  run  forward  to 
the  upper  end  of  the  sewer,  either  requiring  to  be  handled  over 
again  or  flowing  into  the  mouth  of  the  pipe.  If  thrown  upon 
the  bank  and  dried  out,  however,  it  becomes  very  hard  and 
expensive  to  shovel  back.  It  is  probably  better  to  back-fill 
with  it  immediately  at  some  distance  from  the  sewer  under 
construction,  carrying  it  there  by  excavating-machinery  or  in 
wheelbarrows,  or  to  let  it  partly  dry  upon  the  bank  before 
throwing  it  back.  It  is  well  to  have  a  few  short  plank  nailed 
together  to  form  platforms  which  can  be  placed  in  the  trench 
bottom  for  the  men  to  stand  upon,  as  otherwise  they  will  lose 
much  time  digging  themselves  and  each  other  out.  The 
length  of  open  trench  should  be  kept  short  and  the  men 
worked  as  close  together  as  practicable,  and  sub-drain  with  its 
gravel  and  platform  put  in  and  sewer  laid  as  rapidly  as  possi- 
ble. Even  then  the  danger  is  not  over,  as  the  structure  is 
liable  to  be  raised  out  of  place  by  inflowing  quicksand.  A 
pipe  sewer  which  had  been  laid  in  quicksand  and  covered  with 
the  same  material  as  back-filling  has  been  known  to  rise  more 
than  3  feet  overnight,  practically  floating  to  the  surface  of 
the  quicksand.  To  prevent  this  a  plank  may  be  laid  over  the 
sewer  and  braced  down  from  the  sheathing  and  the  pipe  thus 
held  in  place. 

In  the  case  of  a  brick  sewer  the  platform  should  generally 


PRACTICAL    SEWER    CONSTRUCTION.  323 

be  set  upon  piles  (which  can  best  be  driven  by  the  water-jet) 
and  immediately  loaded  with  brick  or  stone  which  is  to  be 
used  in  the  construction.  It  is  advisable  in  most  cases  of 
large  sewers  built  in  quicksand  to  place  close  sheathing  across 
the  trench,  15  to  30  feet  ahead  of  the  completed  sewer,  mak- 
ing a  coffer-dam,  inside  of  which  the  next  section  of  sewer 
is  built.  Meantime  other  cross-sheathing,  15  to  30  feet  still 
further  ahead  of  the  last,  is  being  driven,  together  with 
the  side  sheathing,  and  the  coffer-dam  thus  formed  excavated. 
When  this  is  down  to  grade  and  the  foundation  in,  the  cross- 
sheathing  just  ahead  of  the  completed  sewer  is  removed  and 
the  sewer  continued  into  the  next  section  of  trench.  In  each 
of  these  coffer-dams,  usually  in  one  corner,  is  a  sump  from 
which  the  water  is  kept  pumped.  A  pail  or  barrel  should  be 
used  in  every  sump  in  quicksand  and  the  sand  kept  dug  away 
from  around  it,  as  it  is  very  apt  to  reach  and  stop  the  suction- 
pipe,  from  which  it  is  difficult  to  remove  it.  Gravel  or  fine 
broken  stone  may  be  placed  around  the  barrel  and  carried  a 
few  inches  above  it  to  prevent  the  sand  reaching  it. 

Laying  pipe  sewers  in  quicksand  may  be  even  more  diffi- 
cult than  building  brick  ones.  If  a  platform  foundation  is 
used  there  is  not  sufficient  weight  in  the  pipe  to  hold  it  down 
and  it  must  be  strongly  built  and  braced  down  from  the 
sheathing.  The  following  plan  has  worked  well :  A  sill  of 
4X6  timber  is  laid  near  each  side  of  the  trench,  which  has 
been  brought  as  near  as  possible  to  grade,  and  a  short  piece 
of  plank  is  stood  upon  it  near  one  end.  Two  or  more  men 
then  stand  upon  the  sill  near  this  end  and  work  it  down  to  the 
necessary  depth,  when  the  upright  is  nailed  to  a  brace  or 
ranger  and  the  sill  at  this  point  thus  held  down  to  place.  The 
other  end  is  then  worked  to  place  and  similarly  braced  and 
the  other  sill  treated  likewise.  By  this  time  the  sand  is  prob- 
ably several  inches  deep  over  both  sills.  Cross-planking  for 
the  platform  having  been  sawed  to  length — the  closer  they  fit 


324  SEWERAGE. 

between  the  sheathing  the  better — one  at  a  time  a  place  is 
cleaned  for  them  and  they  are  nailed  to  the  sills  with  close 
joints.  Good  material  is  then  placed  on  this  platform  and  the 
pipe  laid  thereon  and  the  same  material  immediately  back- 
filled around  and  above  it.  When  the  pipe  has  been  laid  to 
the  end  of  the  platform  it  should  be  tightly  plugged,  if  the 
next  platform  is  not  ready  to  continue  laying  (as  it  probably 
will  not  be),  to  keep  out  the  quicksand,  which  may  rise  above 
the  pipe-invert  before  the  laying  is  continued. 

Another  plan  for  laying  sewer-pipe,  and  an  excellent 
one  for  sub-drains,  in  quicksand  is  as  follows:  Two  planks, 
each  about  6  feet  long,  are  stood  upon  edge  a  sufficient  dis- 
tance apart  to  permit  laying  between  them  the  sewer-pipe,  or 
drain-pipe  and  required  broken  stone,  and  a  strip  of  wood  is 
nailed  across  their  tops  at  each  end.  The  other  edges  are 
then  turned  up  and  similarly  treated,  a  bottomless  trough 
being  thus  formed.  A  loose  bottom  is  provided  to  fit  it, 
usually  in  two  or  three  pieces.  The  bottomless  trough  is 
then  placed  in  the  trench  with  the  plank  on  edge  and  worked 
down  into  the  quicksand  until  to  the  necessary  depth  and  in 
the  correct  line,  and  is  braced  down  from  the  sheathing.  The 
sand  is  then  shovelled  out  of  this  and  the  bottom  planks  put 
in,  one  at  a  time,  the  men  standing  on  the  trough  bottom 
until  all  the  planks  are  in  and  secured,  which  is  effected  by 
placing  a  cleat  across  the  bottom  at  each  end  and  fastening  it 
to  the  sides  of  the  trough.  The  sewer,  or  sub-drain  and 
broken  stone,  are  laid  in  this  and  good  material  is  packed 
around  and  over  the  sewer.  This  method  is  also  adapted  to 
dry  running  sand,  where  the  trough  can  generally  be  used 
without  a  bottom. 

Another  method  sometimes  employed  is  to  excavate  the 
quicksand  in  short  sections  somewhat  below  the  pipe-level 
and  refill  it  with  cinders,  or  spread  burlap  over  the  bottom 
and  cover  it  with  gravel,  on  which  the  sub-drain  or  sewer  is  laid. 


PRACTICAL    SEWER    CONSTRUCTION.  325 

Still  another  plan  is  to  drive  tubes  a  few  feet  apart  through- 
out the  entire  trench,  a  few  at  a  time,  their  bottoms  being  all 
about  a  foot  or  two  below  the  pipe  grade,  and  inject  cement 
and  water  under  pressure,  the  cement  filling  the  interstices  of 
the  surrounding  sand  and  forming  an  artificial  stone,  which 
prevents  the  quicksand  from  rising.  The  pipes  are  then 
removed  and  the  trench  excavated.  This  process  is  patented 
and  expensive. 

In  laying  sub-drains  through  wet  soils,  particularly  wet 
sand,  a  great  deal  of  annoyance  and  expense  will  almost 
surely  be  incurred  if  some  plan  is  not  carried  out  for  keeping 
the  pipe  free  from  deposits,  which  will  form  from  the  dirty 
water  flowing  into  the  end  of  the  pipe.  Probably  the  best 
plan  is  to  keep  a  rope  drawn  through  at  least  600  feet  of  the 
pipe,  the  end  being  drawn  forward  through  each  length  as  it 
is  laid.  At  intervals  of  from  10  minutes  to  half  a  day  the 
rope  should  be  pulled  back  and  forth  to  stir  up  the  deposit 
and  keep  it  moving.  It  is  well  to  knot  up  a  light  chain  and  at 
least  once  a  day  tie  it  firmly  to  the  rope  and  draw  this  through 
the  drain  a  few  times.  If  the  rope  is  neglected  for  too  long  a 
time  it  may  become  imbedded  in  the  deposit  and  require  six 
or  eight  men  or  even  a  team  to  draw  it  through  the  pipe.  It 
should  be  amply  strong  for  this.  When  a  section  between 
manholes  is  completed  the  rope  should  be  left  in  until  the 
next  section  is  completed,  as  a  part  of  the  dirt  flowing  through 
the  upper  will  probably  settle  in  the  lower  section.  The  latter 
should  be  cleaned  at  least  once  every  day.  It  may  be  well, 
if  the  deposits  are  considerable,  to  fasten  to  the  rope  in  the 
lower  section  a  strap  to  which  two  or  three  tapering  tin  cans 
are  riveted  (see  Fig.  29).  These  are  drawn  a  little  way  into 
the  pipe,  closed  end  first,  and  then  drawn  back  and  the  dirt 
emptied  from  them.  (If  started  through  the  pipe  mouth  first 
they  would  probably  pile  the  dirt  ahead  of  themselves  into  an 
immovable  mass.)  When  not  in  use  these  should  be  kept  out 


326  SEWERAGE. 

of  the  pipe,  as  should  also  the  knotted  chain  above  mentioned, 
to  permit  the  free  passage  of  water. 

It  is  advisable  to  flush  the  drain  with  comparatively  clean 
water  as  often  as  possible.  This  may  be  done  by  catching 
the  ground-water  by  dams,  as  described  above,  and,  when  the 
drain  has  been  laid  up  to  a  dam,  bailing  the  water  rapidly  from 
this  into  the  drain.  Or  a  plank  may  be  set  across  the  trench 
bottom  just  ahead  of  the  pipe,  so  as  to  catch  any  mud  or 
stones  which  may  be  washed  down  but  permit  the  water  to 


FIG.  29. — APPLIANCE  FOR  CLEANING  SUB-DRAINS. 

flow  over,  and  the  dam  be  broken,  but  kept  under  control,  so 
that  it  can  be  closed  if  desired. 

It  is  well  to  always  keep  in  the  end  of  the  pipe  a  pan  with 
fine  holes  over  the  upper  half  of  its  bottom,  these  holes  form- 
ing the  only  entrance  for  water  to  the  pipe.  Sticks  and  stones 
are  thus  kept  out  of  the  sewer,  as  well  as  the  water  most  thick 
with  mud.  If  the  water  is  clear  the  perforated  part  of  the 
pan  can  be  placed  at  the  bottom.  These  remarks  refer  par- 
ticularly to  sub-drains,  since  water  should  not  be  permitted 
to  rise  above  the  sewer-invert. 

The  entire  system  of  sub-drains  cannot  be  flushed  too 
often  during  construction — by  hose  from  the  fire-hydrants,  if 
possible.  If  a  drain  is  stopped  up  in  which  there  is  no  rope, 
or  the  rope  cannot  be  moved,  a  hole  can  sometimes  be  forced 
through  the  obstruction  by  a  line  of  J-inch  or  i-inch  iron 
pipe.  If  this  is  fastened  by  a  special  bushing  or  otherwise  in 
the  end  of  a  hose  and  water  forced  through  it,  it  can  be  driven 
through  in  almost  every  instance  if  the  friction  between  the 
iron  pipe  and  the  deposited  material  does  not  become  too 
great.  If  the  section  in  which  the  stoppage  occurs  is  not  at 
the  incompleted  end  this  plan  cannot  be  adopted;  but  an  old 


PRACTICAL   SEWER    CONSTRUCTION.  327 

length  of  2^-inch  hose  with  no  coupling  on  one  end  can  be 
placed  at  the  end  of  a  line  leading  from  a  fire-hydrant  to  and 
down  a  manhole,  and  this  end  pushed  into  the  drain;  when 
the  water  is  turned  on  the  hose  can  be  pushed  forward  as  if  it 
were  a  flexible  rod,  and  the  water  from  the  hose  will  wash  the 
obstruction  loose  and  bring  it  back  to  the  manhole,  where  it 
can  be  removed  from  the  sub-drain  well  by  hand,  the  water 
rising  up  and  overflowing  into  the  sewer.  Sand,  gravel,  and 
even  brick-bats  have  been  washed  out  of  drains  by  this 
hydraulic  process. 

When  laying  a  pipe  sewer  the  manhole  is  not  usually  con- 
structed until  the  sewer  has  been  laid  on  each  side  of  it.  In 
quicksand  if  the  trench  is  opened  through  where  the  manhole 
is  to  be  it  will  immediately  fill  up  above  the  sewer.  The  pipe 
must  therefore  be  plugged  at  the  end.  It  is,  for  this  and 
other  reasons,  often  desirable  in  quicksand  to  build  the  man- 
hole before  the  sewer  reaches  it,  openings  for  the  sewer  being 
left  in  the  manhole-wall  at  the  proper  points.  The  excavation 
for  the  manhole  must  be  made  in  a  well-hole  close-sheathed 
for  at  least  a  foot  lower  than  the  sewer-invert.  It  will  be 
found  difficult  to  get  the  bottom  in  with  the  ordinary 
methods,  particularly  if  there  is  a  sub-drain  well  to  be  put  in. 
In  such  a  case  the  following  plan  has  been  used  with  success : 
A  12-  or  1 5 -inch  pipe  with  two  T  branches  of  the  size  of  the 
sub-drain,  temporarily  plugged,  is  lowered  into  position  to  act 
as  the  sub-drain  well,  the  bell  being  up  and  the  branches 
being  placed  at  the  grade  of  the  sub-drain,  which  connects  into 
them.  The  manhole  excavation  having  first  been  carried  to 
the  depth  necessary  for  the  foundation,  this  pipe  may  be 
lowered  by  resting  upon  it  with  the  knees  and  digging  the 
sand  from  the  inside,  care  being  taken  to  keep  it  vertical  and 
in  the  proper  position.  When  it  has  reached  the  required 
depth  the  sand  is  scooped  out  a  little  below  its  lower  end  and 
one  or  two  bucketfuls  of  concrete  placed  there  and  rammed 


328  SEWERAGE. 

(see  Plate  X,  Fig.  9).  It  is  well  to  place  a  board  bottom 
inside  the  pipe  on  top  of  the  concrete  and  to  place  brick  on 
this  to  keep  the  concrete  from  being  forced  up,  the  brick 
being  removed  after  the  concrete  sets.  If  necessary  another 
12-  or  1 5 -inch  pipe  is  placed  upright  in  the  hub  of  this  one. 
A  length  or  two  of  drain-pipe  is  fixed  in  each  branch  of  the 
sub-drain  well  in  a  horizontal  position  and  in  the  proper  line 
to  connect  with  the  sub-drain  when  laid,  and  the  manhole 
bottom  is  then  dug  out  to  the  grade  of  the  bottom  of  the 
foundation  and  concrete  placed  there,  before  the  sand  rises,  in 
small  areas  of  8  or  10  feet  at  a  time.  This  is  done  rapidly  and 
the  concrete  loaded  with  brick,  if  necessary,  to  hold  it  down. 
The  concrete  is  placed  last  where  the  channel  comes  and  a 
split-pipe  invert  is  at  once  forced  down  in  it  to  the  proper 
grade,  and  a  straight-edged  plank  placed  on  edge  in  the  invert 
bottom  and  braced  down  from  the  sheathing  to  hold  it  in 
position.  The  formation  of  the  manhole  bottom  is  then  com- 
pleted and  the  walls  built  in  the  usual  way,  sewer-pipe  being 
built  into  the  manhole-walls  where  the  sewers  are  to  enter  it, 
but  loosely  enough  to  permit  of  sliding  the  pipe  out.  The 
sewer  already  laid  or  to  be  laid  is  carried  through  this  opening 
by  a  pipe  cut  to  the  necessary  length,  the  sheathing  having 
been  cut  away  here  to  permit  this. 

Another  plan  is  to  lay  a  plank  foundation  for  the  concrete, 
one  plank  at  a  time  being  put  in  place  and  fastened  to  the 
sheathing,  thus  forming  of  the  whole  a  tight  box,  in  which  the 
manhole  is  built.  Flush-tanks,  inlets,  and  other  appurte- 
nances can  of  course  be  built  in  the  same  way. 

ART.  T9.     RIVER-CROSSINGS  AND  OUTLETS. 

For  convenience  of  inspection  and  as  permitting  easier 
maintenance  it  is  best  to  carry  a  sewer  across  a  stream  on  a 
bridge  or  trestle,  keeping  its  invert  at  the  hydraulic  gradient ; 


PRACTICAL   SEWER    CONSTRUCTION. 


329 


unless,  of  course,  this  is  below  the  river-bed,  when  the  sewer  will 
occupy  that  position.  Very  often  the  use  of  bridge  or  trestle 
is  impossible  or  prohibitively  expensive,  and  then  an  inverted 
siphon  is  necessary.  In  either  case  the  pipe  will  probably  be 
of  iron  or  wood,  although  a  combination  of  these  with  masonry 
is  sometimes  used.  In  some  instances  it  may  be  better  to 
build  the  siphon  in  tunnel,  when  it  should  be  lined  with  brick 
or  concrete;  or,  as  is  usually  better,  two  or  more  iron  or  wood 
siphon  pipes  may  be  laid  in  the  tunnel,  easy  access  to  them 
being  thus  afforded. 

A  bridge  or  trestle  for  supporting  a  sewer  should  seldom 
be  built  of  wood,  owing  to  the  difficulty  of  providing  for  the 
sewage  when  necessary  renewals  are  being  made.  It  may  in 
some  instances  be  unsafe  to  support  a  sewer  by  an  existing 


FIG.  30.— SEWER  CROSSING  CREEK  ABOVE  WATER. 

bridge,  owing  to  the  great  increase  of  load  thus  brought  upon 
it.  (An  1 8-inch  cast-iron  pipe  flowing  full  of  sewage  will 
weigh  about  225  pounds  per  lineal  foot.)  The  bridge  has  in 
some  cases  been  relieved  of  this  weight  by  constructing  the 
pipe  in  the  form  of  an  arch,  but  this  is  not  generally  advis- 


33°  SEWERAGE. 

able.  A  simple  design  for  a  short  span,  as  over  a  creek,  is 
shown  in  Fig.  30;  or  the  pipe  could  be  supported  inside  an 
iron  or  steel  box  girder  of  suitable  size  and  strength.  There 
is  no  danger  of  the  sewage  freezing  unless  the  pipe  is  exposed 
for  a  stretch  of  many  hundred  feet. 

If  the  distance  to  be  crossed  is  more  than  200  or  300  feet 
the  inverted  siphon  will  in  most  cases  be  found  advisable. 
Its  construction  under  water  will  be  similar  to  that  of  river- 
crossings  laid  to  grade,  except  that  in  the  latter  the  most 
advantageous  depth  cannot  be  chosen. 

The  joints  and  pipe  of  subaqueous  siphons  and  other 
sewers  should  be  perfectly  water-tight,  as  it  will  be  necessary 
at  times  to  empty  them  of  sewage  for  inspection.  They  should, 
if  of  small  pipe,  be  laid  to  as  straight  a  line  and  grade  as  any 
part  of  the  system.  If  they  are  sufficiently  large  to  be  entered 
this  is  not  so  important.  They  should  never  be  laid  on  the 
bed  of  the  river,  but  always  beneath  it. 

.  For  a  sewer  up  to  30  or  36  inches  diameter  cast-iron  pipe 
with  lead  or  hardwood  joints  may  be  used.  The  trench  is 
excavated  at  least  1 8  to  24  inches  wider  than  the  pipe  and  6 
to  12  inches  below  its  grade.  Inside  this  trench  the  pipe  is 
placed  and  suspended  to  grade  or  blocked  up  at  intervals. 
The  joints  are  made  and  concrete  is  placed  under  the  pipe  at 
all  points,  completely  filling  the  trench  for  a  distance  of  2  or 
3  feet  above  the  pipe,  or  to  the  surface  of  the  river-bed,  it  all 
being  thoroughly  rammed.  If  the  concrete  does  not  reach 
the  bed  of  the  river  it  is  well  to  throw  loose  stone  over  and 
along  each  side  of  it. 

If  the  river  is  not  very  deep,  or  a  time  can  be  chosen  when 
such  is  the  case,  it  is  in  many  instances  practicable  to  confine 
it  to  half  the  width  of  the  bed,  at  the  point  of  crossing,  by  an 
earthen  embankment  or  timber  coffer-dam,  or  combination  of 
both,  carried,  just  up  stream  from  the  line  of  sewer,  from 
above  the  water-line  out  to  mid-channel,  across  the  line  of 


PRACTICAL   SEWER    CONSTRUCTION.  331 

sewer,  and  back  again  to  the  bank  a  few  feet  lower  down. 
The  enclosed  space  is  then  pumped  out,  the  trench  dug  and 
sheathed,  the  pipe  and  concrete  put  in  position  and  covered, 
and  the  dam  removed  and  a  similar  one  placed  upon  the  oppo- 
site side  of  the  river,  which  then  flows  over  the  pipe  already 
laid.  In  many  cases  the  best  form  of  dam  for  sewer-crossings 
is  made  by  permitting  the  close  sheathing  of  the  pipe-trench 
to  serve  also  as  a  dam,  extending  above  the  water-surface  and 
backed  by  earth  embankment.  A  brief  statement  of  the 
details  of  carrying  out  this  plan,  which  must,  however,  be 
varied  under  different  conditions,  is  given. 

The  sewer  having  been  laid  up  to  the  river-bank,  a  stout 
stake  is  driven  into  the  river-bed  about  10  feet  from  the  end 
of  this  and  in  line  with  the  down-stream  side  of  the  trench. 
If  necessary  another  is  driven  a  few  feet  lower  down  and  a 
brace  set  from  the  foot  of  this  to  the  top  of  the  former.  A 
frame  of  rangers  and  braces  is  built  upon  the  bank,  of  dimen- 
sions proportioned  for  the  proposed  trench,  and  floated  to 
place  in  line  with  the  trench  already  dug,  the  inner  end  being 
fastened  in  position  against  the  end  of  this  trench  and  the 
outer  being  held  by  the  stake  just  mentioned.  Sheathing  is 
then  driven  on  both  sides  and  the  end  of  this  frame  (the  end 
braces  are  flush  with  the  ends  of  the  rangers)  as  deep  as  is 
possible  before  excavating  is  begun,  and  earth  banked  against 
the  outside  of  it.  The  water  is  then  pumped  out  and  the 
trench  excavated,  the  sheathing  being  kept  driven  as  low  as 
possible,  additional  rangers  and  braces  being  added,  and  the 
excavated  material  thrown  just  outside  of  it.  When  this 
trench  is  at  grade  the  pipe  is  laid,  concrete  put  in,  and  trench 
back-filled  ahead  to  cross-sheathing  which  has  been  set  just 
back  of  the  end  of  the  pipe.  Another  frame  has  meantime 
been  started  just  ahead,  sheathing  driven,  and  outer  embank- 
ment made.  The  cross-sheathing  between  the  new  and  the 
completed  trench  is  drawn  and  the  excavation  continued. 


332  SEWERAGE. 

Cross-sheathing  is  set  at  frequent  intervals  and  the  trench  filled 
up  to  it  to  reduce  the  length  of  open  trench  which  must  be 
kept  free  of  water.  It  is  advisable  not  to  cut  off  the  sheath- 
ing and  remove  the  embankment  at  any  point  until  the  con- 
struction is  completed  to  mid-stream.  It  will  usually  be 
necessary  to  keep  a  pump  going  constantly  during  construc- 
tion. If  the  stream  is  subject  to  freshets  it  may  be  well  to 
set  the  pump  upon  a  flat-boat  anchored  against  the  up-stream 
sheathing.  The  boiler  may  be  kept  upon  this  boat  or  upon 
the  bank,  the  steam-pipe  in  the  latter  case  being  carried  along 
the  sheatning. 

If  the  bed  of  the  river  is  gravelly  considerable  trouble  may 
be  experienced  from  water  leaking  into  the  trench,  the  enter- 
ing water  having  perhaps  passed  into  the  ground  many  feet 
from  the  sheathing.  The  embankment  may  in  such  a  case 
be  carried  as  far  as  possible  from  the  sheathing  on  every  side, 
or  a  thin  layer  of  fine  sand,  sandy  loam,  or  loamy  clay  may  be 
spread  over  the  bottom  for  50  or  75  feet  above  and  below  the 
trench.  Also  manure,  brewery-meal,  etc.,  has  been  used  to 
stop  up  the  pores  of  the  gravel.  Heavy,  closely  woven 
canvas  is  excellent  for  use  in  such  a  case,  in  large  squares  or 
strips  tightly  sewed  together,  one  end  being  fastened  above 
water  against  the  outside  of  the  sheathing,  the  other  anchored 
by  stones  or  other  weights  beyond  the  part  of  the  bed  which 
is  giving  trouble. 

An  excellent  material  for  the  embankments  is  a  puddle  of 
clay,  sand,  and  gravel.  Clay  alone  is  almost  useless.  Fine 
and  coarse  sand  mixed,  with  or  without  gravel,  is  better  than 
clay  alone.  All  sticks,  roots,  and  large  stones  should  be 
removed  from  this  puddle,  and  anything  which,  reaching 
through  the  embankment,  may  offer  a  course  for  the  water. 
If  puddling  material  is  scarce  a  double  row  of  sheet-piling  may 
be  carried  around  the  work,  the  two  rows  being  from  2  to  5 
feet  apart,  braced  together  only  at  the  top,  and  the  space 


PRACTICAL   SEWER    CONSTRUCTION. 


333 


between  them  filled  with  puddle  well  worked  and  rammed. 
Experience  in  this  class  of  work  is  almost  essential  to  its 
proper  prosecution,  and  written  directions  can  give  only  the 
barest  outlines  for  meeting  but  a  few  of  the  difficulties  which 
may  be  encountered.  Pluck,  foresight,  a  fertility  in  expedi- 
ents, and  common  sense  are  prime  requisites  for  this  work. 
The  water  must  never  for  an  instant  be  allowed  to  get  the 
upper  hand.  If  nothing  else  is  at  hand  the  very  clothes  off 
one's  back  should  be  taken  to  stop  a  leak  temporarily,  should 


FIG.  31. — COFFER-DAM  PUDDLE- WALLS. 

one  unexpectedly  develop  in  an  embankment.  Never  permit 
a  brace,  stick,  or  any  object  to  extend  through  an  embank- 
ment or  puddle-trench  or  -wall.  If  a  trench  surrounded  by 
water  shows  signs  of  collapsing  from  outside  pressure  and  no 
material  for  additional  rangers  and  braces  is  at  hand  the 
trench  can  sometimes  be  saved  by  allowing  water  to  fill  it,  and 
then,  when  the  material  has  been  obtained,  the  water  can  be 
pumped  down  and  bracing  put  in  as  it  lowers.  But  this  is  a 
somewhat  desperate  remedy. 

An  outlet  for  the  Massachusetts  Metropolitan  Sewerage 
System  at  Deer  Island,  in  5  to  10  feet  of  water,  was  built  in 
open  trench,  with  double  sheathing  and  puddle,  as  in  Fig.  31. 
The  sewer  was  6  feet  3^  inches  inside  diameter  and  the  trench 
10  feet  wide  on  the  bottom,  concrete  being  carried  from  about 
i  foot  beneath  the  sewer  to  an  average  of  4  feet  above  it. 
"  The  cost  of  the  trench,  including  coffer-dam,  sheeting  left 


334  SEWERAGE. 

in  place,  and  back-filling,  was  $44  per  lineal  foot."  (Engineer- 
ing News,  vol.  XXXI,  page  121.)  The  material  through 
which  the  trench  was  carried  was  sand  and  gravel.  The  work 
was  done  by  day  labor. 

If  the  trench  is  in  rock  or  a  tight  coffer-dam  cannot  be 
made  except  at  great  expense  it  may  be  cheaper  and  better 
to  resort  to  divers.  When  not  in  rock,  however,  the  exca- 
vation of  the  trench  should  be  done  by  a  dredge  or  similar 
appliance  if  possible,  as  divers'  labor  is  very  expensive. 

The  end  of  an  outlet  which  discharges  at  some  distance 
from  the  shore  of  a  stream  or  other  body  of  water  should  be 
so  located  and  designed  that  currents,  tides,  or  storms  cannot 
wash  it  full  of  sand  or  mud,  that  it  cannot  settle  down  into 
the  bottom,  that  it  cannot  be  undermined  by  tides  or  cur- 
rents, and  that  the  sewage  discharged  will  not  settle  in  front 
of  it  and  block  the  outlet.  This  may  be  accomplished  by 
laying  the  sewer  in  a  trench  as  described  above,  and  at  the 
very  end  placing  a  right-angled  bend  pointing  upward  and 
extending  I  to  3  feet  above  the  bottom,  this  upright  pipe 
being  surrounded  with  a  cone-shaped  mass  of  concrete.  Or 
the  end  of  the  sewer  may  be  continued  straight,  but  raised 
gradually  until  the  outlet  is  2  or  3  feet  above  the  bottom,  it 
being  supported  between  two  rows  of  piles  back  to  where  it 
has  2  or  3  feet  of  covering. 

It  is  not  so  necessary  that  an  outlet  pipe  be  straight  in 
line  and  grade  provided  the  grade  continually  falls  at  a  suffi- 
cient rate.  The  use  of  flexible-jointed  iron  pipe,  such  as  is 
frequently  employed  for  water-pipes  at  river-crossings,  may 
often  be  used  for  sewer-outlets.  They  should  be  properly 
protected  by  concrete,  riprap  covering,  or  piling.  For 
furnishing  and  laying  2200  feet  of  24-inch  iron  pipe  with 
Ward  flexible  joints  in  a  bottom  consisting  of  sand,  gravel, 
loose  and  solid  rock,  in  a  trench  having  an  average  depth  of 
4  feet,  the  depth  of  water  at  high  tide  being  1 1£  to  30  feet, 


PRACTICAL   SEWER    CONSTRUCTION.  335 

from  $16.85  Per  foot  to  almost  double  this  amount  was  bid  in 
1898.      In  ordinary  river- work  the  cost  should  be  much  less. 

Whenever  subaqueous  work  of  any  considerable  extent  is 
being  done  it  will  be  well  to  have  a  diver's  outfit  on  hand,  as 
its  immediate  use  may  sometimes  effect  a  saving  of  the  work 
from  serious  damage. 

ART.  80.     CROSSING  RAILROADS  AND  CANALS. 

Railroads  should  be  crossed  with  particular  care,  both  that 
no  accident  may  occur  to  either  the  workmen  or  to  passing 
trains,  and  because  of  the  difficulty  of  afterward  repairing 
breaks  or  defects  at  such  points.  This  applies  also  to  sewers 
constructed  in  or  close  to  the  foot  of  railroad  embankments. 

It  is  not  advisable  to  tunnel  under  a  railroad  unless  the 
sewer  runs  quite  deep  and  the  material  is  stable.  A  settling 
of  the  ground  above  the  tunnel  might  prove  disastrous  to 
trains,  and  this  settling  is  extremely  probable,  owing  to  the 
jarring  of  passing  trains.  If  there  is  a  culvert  under  the  road 
through  which  the  sewer  can  be  passed  it  will  often  be  well 
to  take  advantage  of  this,  if  only  a  slight  detour  be  necessary 
in  order  to  do  so. 

If  the  sewer  is  to  pass  under  the  railroad  in  open  cut  each 
rail  should  be  first  supported  by  bridge  timbers,  beams,  or 
iron  rails  placed  under  the  ties  lengthwise  of  the  track  and 
extending  10  to  20  feet  beyond  each  side  of  the  proposed 
trench.  For  a  trench  4  to  6  feet  wide  a  12  X  12  bridge 
timber  25  or  30  feet  long  may  be  used.  A  heavy  steel  rail 
may  be  used  under  the  same  conditions,  but  is  not  generally 
so  stiff.  Each  beam  or  rail  is  placed  in  a  trench  dug  under 
the  ends  of  the  railroad-ties,  just  sufficiently  deep  and  wide 
to  enable  it  to  be  placed  under  the  track-rail.  Hardwood 
plank  are  then  driven  between  this  and  the  ground  and 
wedges  driven  between  each  tie  and  the  beam.  The  trench 


SEWERAGE. 

is  then  excavated,  horizontal  sheathing  being  used.  The 
earth  excavated  cannot  be  thrown  upon  the  surface  unless  the 
track  is  temporarily  out  of  use.  It  may  be  handled  by  a 
cable-way  excavator  which  swings  sufficiently  high  to  clear  all 
trains.  The  buckets  for  this  it  will  be  well  to  have  large — 
those  holding  a  cubic  yard  will  do — that  the  number  of  trips 
may  be  lessened.  The  back-filling  can  be  returned  in  the 
same  way  and  should  be  most  thoroughly  tamped. 

Another  method  of  handling  the  earth,  particularly  ap- 
plicable where  there  are  but  two  or  three  tracks,  is  to  throw 
the  excavated  material  beyond  the  outside  track  by  one  or 
two  handlings,  a  space  for  this  having  been  left  clear  of  earth 
by  previous  management.  If  the  trench  is  shallow  and  as 
short  a  length  as  practicable  opened  at  a  time  it  may  even 
be  possible  to  throw  the  excavated  earth  directly  onto  the 
completed  sewer,  but  if  this  is  done  only  a  very  few  men  can 
be  worked  at  this  point. 

After  the  completion  of  the  work  with  thoroughly  tamped 
back-filling  the  trench  should  be  wet  down  every  two  or  three 
days  for  several  weeks,  the  bridge  timbers  or  rails  being  left 
under  the  ties  meantime.  Just  before  each  wetting  earth 
should  be  placed  and  tamped  on  the  filled  trench  to  2  or  3 
inches  above  the  ties.  When  the  trench  shows  no  settlement 
after  a  wetting  down  the  supporting  timbers  or  rails  may  be 
removed. 

For  small  sewers  it  will  be  well  to  use  iron  pipe  with  lead 
joints  for  railroad-crossings,  and  for  large  sewers  the  arch  and 
side 'walls  should  be  reinforced  (see  Plate  VI,  Fig.  8).  In 
general  it  is  better  to  place  no  manhole  or  other  appurtenance 
between  or  within  several  feet  of  any  tracks. 

A  trench  in  or  near  a  railroad  embankment  is  subject  to 
the  jarring  of  the  trains  and  needs  to  be  carefully  sheathed. 
This  is  sometimes  difficult  if  the  trench  be  wholly  or  partly 
upon  the  slope  of  the  embankment,  since  there  is  nothing 


PRACTICAL    SEWER    CONSTRUCTION. 


337 


FIG.  32. — SHEATHING  ON  STEEP 
SLOPES. 


opposite  the  upper  ranger  on  the  up-hill  side  against  which 
to  brace  it.  It  will  not  usually  be  practicable  to  place  a  slop- 
ing brace  from  this  to  a  lower  ranger  on  the  opposite  side. 
A  better  plan  would  be  to  brace  the  sheathing  against  posts 
driven  at  intervals  a  little  distance  from  the  lower  side  of  the 
trench  and  throw  all  the  excavated  material  against  this  side. 
The  sheathing  on  the  lower 
side  at  least  should  be  left  in 
and  protruding  a  short  distance 
above  the  ground  after  the  work 
is  completed,  to  prevent  the 
back-filling,  which  should  all 
be  thoroughly  hand-rammed, 
from  being  washed  down  the 
bank  by  rain. 

It  is  not  impossible  to  con- 
struct a  sewer  under  a  canal, 
raceway,  or  other  body  of  water  retained  by  embankments 
without  drawing  off  the  water  or  interfering  with  its  service, 
but  it  is  much  easier  and  safer  to  do  this  work  when,  if  ever, 
the  water  is  out.  The  construction  of  a  system  can  generally 
be  so  managed  that  all  canal-crossings  may  be  made  in  winter 
while  the  water  is  out,  even  if  no  other  part  of  the  system  is 
constructed  at  that  time.  A  raceway  can  in  many  cases  be  car- 
ried over  the  excavation  temporarily  by  a  flume  extending  for 
some  distance  in  each  direction  from  it.  Care  must  be  taken 
to  prevent  the  water  following  the  outside  of  this,  for  which 
purpose  close  sheet-piling  may  be  used  to  advantage,  being 
driven  across  the  raceway  at  each  end  of  the  flume  and 
making  a  tight  joint  with  it. 

A  sewer  under  or  near  a  canal  should  be  of  iron  pipe, 
unless  too  large,  when  concrete  may  be  used,  made  very 
strong  and  extra  thick — say  I  part  Portland  cement,  2  parts 
sand,  3  parts  broken  stone,  with  a  5O-per-cent  increase  in 


33$  SEWERAGE. 

thickness  over  ordinary  localities.  If  iron  pipe  be  used  cast- 
iron  flanges  made  in  halves  should  be  bolted  on  the  pipe  at 
intervals,  a  thin  lead  strip  being  placed  between  the  pipe  and 
the  flange  casting  to  make  a  water-tight  joint,  or  lead  being 
calked  into  bells  on  the  flange,  as  in  the  case  of  a  sleeve-joint. 
Two  or  three  of  these  flanges  should  be  placed  in  each  em- 
bankment and  others  10  or  15  feet  apart  through  the  canal. 
All  space  under,  around,  and  above  the  pipe 
should  be  thoroughly  filled  with  puddled 
clay,  gravel,  and  sand  carefully  rammed.  If 
clay  cannot  be  had  loam  may  be  used,  free 
from  roots  or  "  muck."  A  good  proportion 
FIG.  33.— FLANGE  ^or  these  materials  is  I  part  of  clay,  ij  parts 
FOR  PIPE  IN  EM-  of  sand,  and  4  parts  of  gravel,  thoroughly 
BANKMENT.  mixed  before  placing  in  the  trench.  If  the 
sewer  is  of  concrete  flanges  of  the  same  material  may  be 
built  around  the  barrel  at  intervals;  or  the  flanges  may  be  of 
stone  masonry,  water-tight,  with  rough  face.  The  flange, 
whether  of  iron,  concrete,  or  stone,  is  better  the  rougher  it 
is.  It  would  be  well  to  imbed  rough  stones  in  the  entire 
outside  of  a  concrete  sewer  under  a  canal  to  prevent  the 
water  following  the  surface  and  creating  a  leak. 

If  the  earth  over  the  sewer  in  the  canal-bed  is  shallow  or 
is  not  absolutely  impervious  there  must  be  sufficient  weight 
in  or  attached  to  the  sewer  to  prevent  it  from  floating  if 
empty.  A  24-inch  iron-pipe  crossing  only  two  or  three  feet 
under  a  canal  has  been  known  to  break  in  two  at  a  joint  and 
a  part  of  it  rise  through  the  thin  earth  covering  into  the  water 
above  on  account  of  the  hydrostatic  pressure  brought  to  bear 
by  seepage-water.  It  must  be  remembered  that  an  empty 
iron  pipe  36  inches  diameter,  for  instance,  to  weigh  as  much 
as  the  displaced  water  must  be  if  inches  thick.  Conse- 
quently the  heavier  weights  of  iron  pipe  should  be  used,  or 
else  they  should  be  weighted  down  with  concrete,  iron  cast- 


PRACTICAL    SEWER   CONSTRUCTION.  339 

ings,  or  in  some  other  way.     It  will  usually  be  found  cheaper 
to  use  the  heavy  pipe. 

If  it  is  necessary  to  pass  a  sewer  under  a  body  of  water  in 
tunnel  this  may  require  the  use  of  compressed  air,  shields, 
etc.,  and  should  not  be  undertaken  without  the  advice  of  an 
expert  in  such  work. 


PART  III. 

MAINTENANCE. 


CHAPTER    XIV. 
HOUSE-CONNECTIONS   AND   -DRAINAGE. 

ART.  81.     NECESSITY  FOR  INTELLIGENT  MAINTENANCE. 

IT  is  the  too  general  rule  that  when  a  city  has  constructed 
a  system  of  sewers  it  considers  its  duty  done,  and  permits  any 
kind  of  connection  to  be  made  with  them,  by  anybody  and  in 
any  way,  and  takes  no  more  thought  of  its  sewers  until  com- 
pelled to  do  so  by  some  obnoxious  conditions  therein.  This 
is  all  totally  wrong,  and  even  criminal.  While  it  is  not 
probable  that  any  well-designed  and  constructed  sewerage 
system  will  ever  become  "  worse  than  no  system  at  all  "  or 
an  "  elongated  cesspool,"  it  will  not  work  at  its  best  efficiency 
and  free  from  objectionable  conditions  if  unattended  to,  any 
more  than  would  any  mechanism. 

Moreover,  a  considerable  expense  has  been  incurred  to 
provide  sanitary  sewerage  for  the  citizens,  but  if  careless  or 
penurious  landlords  or  plumbers  or  ignorant  householders  are 
permitted  to  construct  between  the  sewer  and  the  house,  or 
in  the  latter,  cheap  and  unsanitary  house-connections,  -drains, 
and  plumbing  fixtures  the  health  of  the  citizens  is  endangered 

340 


HOUSE-CONNECTIONS  AND    -DRAINAGE.  341 

and  complete  return  for  the  outlay  for  sewers  is  not  received. 
No  dread  of  paternalism  should  interfere  with  the  proper  per- 
formance by  the  city  of  its  manifest  duty  to  require  that  all 
""  sanitary  "  piping  and  fixtures  throughout  the  city  are  sani- 
tary, and  the  sewers  should  be  in  the  charge  of  an  experienced 
officer  who  is  held  responsible  for  their  cleanliness  and 
efficiency. 

The  first  necessity  for  this  oversight  will  come  with  the 
connection  of  the  dwellings  to  the  sewers. 

ART.  82.    REQUIREMENTS  OF  SANITARY  HOUSE-DRAINAGE. 

No  house-connections  should  be  attached  to  a  sewer 
except  in  the  presence  and  under  the  direction  of  a  city 
inspector  and  by  a  party  who  is  under  bond  to  follow  the 
city's  regulations  for  such  work. 

No  house  should  be  allowed  to  connect  with  the  sewer 
until  its  construction  is  entirely  completed,  including  plaster- 
ing and  sanitary  fixtures,  owing  to  the  danger  that  mortar  and 
rubbish  may  otherwise  be  admitted  to  the  sewer. 

No  connection  should  be  made  with  a  sewer  except  at  a 
branch  provided  for  that  purpose.  If  there  should  be  no 
branch  within  a  short  distance  one  may  be  inserted  in  a  brick 
sewer  by  cutting  through  its  wall  and  building  a  slant  firmly 
in  place  or,  in  a  pipe  sewer,  by  removing  a  pipe  and  inserting 
a  branch  pipe  in  its  place.  If  3-foot  lengths  of  pipe  were  laid 
in  the  sewer  a  few  3-foot  lengths  of  branch  pipes  may  be  kept 
on  hand  for  this  purpose.  (Branch  pipes  are  generally  used 
in  2-foot  lengths.)  To  remove  a  pipe  from  a  sewer  it  may  be 
broken  to  pieces  with  a  hammer,  care  being  taken  not  to  crack 
the  adjacent  pipe.  Then,  with  a  cold-chisel  used  with  some 
rare,  the  upper  half  of  the  bell  facing  this  opening  is  broken 
away  and  likewise  the  upper  half  of  the  bell  of  the  branch 
pipe  to  be  inserted.  This  is  then  dropped  into  place  with 


342  SEWERAGE. 

the  branch  on  the  wrong  side  and  revolved,  thus  bringing  to 
the  top  of  the  sewer  that  part  of  both  pipes  where  the  bell  is 
wanting.  The  joint  is  then  made,  Portland  cement  being 
substituted  for  the  missing  portions  of  the  bells. 

In  breaking  the  cap  or  plug  out  of  a  sealed  branch  care 
must  be  taken  not  to  break  any  part  of  the  pipe.  If  broken 
the  pipe  should  be  replaced  by  a  new  one,  as  above.  If  the 
branch  is  cracked  it  may  be  left  in,  but  should  be  surrounded 
with  rich  cement  concrete  well  compacted. 

It  is  absolutely  not  permissible  to  cut  a  hole  into  a  pipe 
sewer  and  insert  the  house-connection  therein,  as  it  is  almost 
impossible  to  obtain  a  junction  which  will  not  leak  or  to 
prevent  the  connection-pipe  from  protruding  into  the  sewer. 

The  house-connection  should  never  be  larger  than  the 
branch  which  it  enters,  but  should  preferably  be  smaller.  A 
4-inch  pipe  is  large  enough  for  any  residence  or  small  hotel 
or,  in  general,  for  90  per  cent  of  all  the  buildings  in  most 
cities.  On  a  grade  of  I  :  40  it  should  carry  the  simultaneous 
discharge  of  ten  or  more  water-closet  flushes,  or  that  of  two 
large  bath-tubs  when  emptying  themselves  in  two  minutes. 
This  connection  may  be  of  vitrified  clay  pipe  from  the  sewer 
to  a  point  5  or  6  feet  outside  of  the  cellar  wall.  It  should  be 
laid  to  as  perfect  line  and  grade  as  was  the  sewer  itself,  the 
fall  of  I  :  40  being  the  minimum  allowed  under  any  but 
exceptional  circumstances.  If  a  uniform  grade  from  the  sewer 
to  inside  the  cellar  is  not  obtainable  or  desirable,  or  if  this 
distance  be  more  than  100  feet,  it  is  advisable  to  place  an  in- 
spection-hole at  the  fence-line  or  at  some  other  convenient 
point  (see  Plate  XI,  Fig.  10),  the  grade  and  line  being  straight 
each  way  from  this  to  both  sewer  and  house.  If  the  pipe 
branches  before  reaching  the  house  an  inspection-hole  should 
be  placed  at  the  junction.  The  joints  of  the  house-connection 
should  be  of  cement,  and  it  should  be  of  equally  as  good 
material  as,  and  laid  in  every  way  according  to  the  methods 


HOUSE-CONNECTIONS  AND   -DRAINAGE.  343 

used  for,  the  sewer.  In  made  ground  or  quicksand,  or  where 
trees  are  near  the  pipe,  or  the  latter  passes  near  a  well  or 
cistern,  the  connection  should  be  of  iron  water-  or  gas-pipe 
{not  "  plumbers'  pipe  ")  with  lead  joints. 

From  a  point  5  or  6  feet  outside  the  building  into  and 
through  this  the  main  pipe  should  be  of  iron,  and  should 
extend  vertically  to  and  through  the  roof,  its  upper  end,  down 
to  a  few  feet  below  the  roof,  being  preferably  enlarged  some- 
what. The  top  should  be  at  a  distance  from  any  chimney 
and  above  any  garret  or  other  windows,  and  should  not  be 
furnished  with  a  cowl,  quarter-  or  half-bend,  or  any  other 
device.  All  fixtures  in  the  house  discharge  into  this  pipe, 
the  intersections  being  by  means  of  Y's  and  not  T's. 

So  far  all  authorities  agree.  But  the  general  arrangement 
of  traps  and  ventilation-pipes  is  a  point  upon  which  many  of 
them  differ.  The  principal  point  of  difference  is  as  to 
whether  the  pipe  should  be  furnished  with  a  trap  between  the 
sewer  and  the  vertical  "  soil-pipe."  Most  agree  that  a  trap 
should  be  placed  just  below  each  fixture,  although  a  few 
would  dispense  with  this  and  rely  upon  one  main  trap  only. 
{See  "  The  Single  Trap  System  of  House  Drainage,"  Trans- 
actions Am.  Soc.  Civil  Engineers,  vol.  xxv,  page  394.) 
Some  trap  is  desirable,  if  for  no  other  reason  than  to  prevent 
long  sticks,  bones,  knives  and  forks,  and  other  large  articles 
from  being  carried  to  the  sewer.  Most  sanitarians  would 
ventilate  each  trap  by  connecting  the  end  furthest  from  the 
inlet  with  a  main  vent-pipe  leading  through  the  roof. 

The  object  of  the  main  trap,  which  is  generally  placed 
just  inside  the  cellar  wall,  is  to  exclude  the  air  of  the  sewer 
from  the  building.  As  has  been  previously  stated,  however, 
the  house-connection  and  soil  pipes  are  in  most  cases  much 
more  foul  than  the  sewer,  and  the  danger  lies  in  them  rather 
than  in  the  sewer.  The  vertical  soil-pipe,  on  account  of 
the  spraying  action  of  falling  water,  becomes  fouler  and  is 


344  SEWERAGE. 

more  difficult  to  clean  than  almost  any  other  part  of  a  sewer- 
age system.  Hence  the  author  can  see  little  if  any  advantage 
in  the  presence  of  the  main  trap;  none,  certainly,  if  this  be 
not  vented  on  both  ends  to  prevent  its  seal  being  forced  by 
a  compression  of  the  sewer-air  due  to  a  sudden  discharge  into 
the  sewer  from  a  near-by  connection  or  some  other  cause,  and 
to  prevent  a  forcing  of  the  traps  throughout  the  house  by  the 
compression  of  air  in  the  soil-pipe  caused  by  a  considerable 
flush  of  water  from  a  fixture  on  the  upper  .floors;  also  to- 
admit  fresh  air  to  the  house-piping.  Many  excellent  authori- 
ties, however,  advise  the  use  of  the  main  trap. 

The  object  of  continuing  the  soil-pipe  through  the  roof  is 
to  allow  the  foul  air  from  below  to  pass  upward  through  it, 
and  there  seems  to  be  little  objection  to  permitting  the  purer 
air  from  the  sewer  to  occasionally  take  the  same  course,  and" 
even  perhaps  some  advantage  from  its  diluting  effect. 

Whichever  the  plan  adopted,  if  the  workmanship  and 
material  are  of  the  best  there  is  probably  little  danger  to  be 
feared.  If  vent-pipes  are  used  on  a  main  trap  these  should 
terminate  at  a  distance  of  at  least  10  feet  from  any  window  or 
door,  and  in  such  a  manner  that  they  cannot  be  sealed  by 
dirt,  snow,  ice,  or  frost  collecting  around  the  upper  ends  from 
the  damp  sewer-air. 

"  Every  trap  and  dead-space  in  water-closets  must  be 
separately  vented  at  the  top  of  the  outer  bend,  the  branch, 
vents  connecting  with  the  main  vent,"  which  should  be  car- 
ried from  the  lowest  trap  up  through  the  roof.  This  prevents 
siphoning  of  the  traps  by  water  plunging  down  the  soil-pipe 
from  a  higher  closet  or  tub,  and  offers  escape  for  any  foul  air 
forming  in  any  of  the  soil-pipes. 

Authorities  agree  that  water-closets  must  not  be  connected 
directly  with  the  water-supply  pipes,  but  should  be  flushed 
through  an  intermediate  tank  or  tanks  or  similar  appliance; 
that  roof-water  leaders  should  never  be  connected  directly^ 


HOUSE-CONNECTIONS  AND    -DRAINAGE.  345 

with  the  house-connection  pipe  without  an  intermediate  trap; 
and  that  all  pipes  and  sanitary  fixtures  of  whatever  kind 
should  be  everywhere  accessible  for  examination,  and  should 
not  be  walled  or  even  boxed  in.  The  water-closets  should 
never  be  placed  in  rooms  not  receiving  light  and  air  directly 
from  outdoors,  or  at  the  very  least  from  a  large  air-shaft, 
through  a  window  having  at  least  4  or  5  square  feet  area. 

All  piping  in  and  near  the  house  should  be  of  iron. 
Wrought  iron  with  screw-joints  is  preferable  to  cast  iron. 
The  use  of  lead  pipe  is  not  advisable,  except  in  short  exposed 
lengths,  as  it  may  be  punctured  by  nails  or  gnawed  by  rats 
and  mice,  and  is  apt  to  sag  into  unnecessary  running  traps. 
Where  the  pipe  passes  through  the  cellar  wall  this  should  be 
arched,  leaving  a  space  of  two  or  three  inches  around  the 
pipe  to  prevent  the  breaking  of  the  pipe  by  a  settlement  of 
either  it  or  the  wall. 

The  house-connection  should  be  suspended  upon  the  side 
walls  after  entering  the  cellar,  and  should  never  be  placed 
under  the  cellar  floor,  unless,  when  this  is  unavoidable,  it  be 
placed  in  a  shallow  trench  having  brick  or  stone  walls  and  with 
a  removable  top  forming  part  of  the  cellar  floor.  The  soil- 
pipe  should  have  only  easy  curves  and  Y's,  no  angles  or  T's 
anywhere. 

Water-closet  tanks  should  discharge  not  less  than  5  gallons 
with  each  flush,  the  pipes  leading  from  these  to  the  closets 
being  not  less  than  \\  or  I  j-  inches.  No  overflow  from  any 
cistern,  tank,  or  refrigerator  should  discharge  into  any  soil-  or 
waste-pipe,  but  into  a  trapped  sink  or  bowl  connected  there- 
with, the  end  of  the  discharge-pipe  being  at  least  3  inches 
above  the  water  in  said  sink  or  bowl.  There  should  be  no 
wooden  wash-tubs  or  sinks.  Grease-traps,  if  used,  should  be 
cleaned  out  once  a  week.  No  "  bell  trap  "  or  removable 
strainer  should  be  placed  in  sinks  or  tubs.  All  iron  pipes 
used  as  drains  or  soil-pipes  should  be  coated  inside  and  out 


SEWERAGE. 

with  coal-tar  varnish,  or  asphalt,  or  better  still  with  enamel. 
A  hand-  and  inspection-hole  should  be  placed  in  the  house- 
connection  just  inside  the  cellar  wall,  and  outside  the  main 
trap  if  one  be  used. 

Every  system  of  house-drains  and  soil-pipes  should  be 
tested  by  water-pressure  to  at  least  10  pounds  before  being 
accepted  or  used.  (See  also  "  House  Drainage  and  Sanitary 
Plumbing,"  and  "  Sanitary  Engineering,"  by  Wm.  P. 
Gerhard.) 

To  insure  that  the  above  requirements  are  met  by  every 
system  of  house-drainage — and  this  should^  insured — regula- 
tions embodying  them,  and  such  others  as  are  thought  desir- 
able, should  be  drawn  up,  and  an  inspector  or  inspectors 
appointed  to  examine  and  approve  of  all  plans  for  house- 
drainage  and  to  see  that  these  are  faithfully  carried  out. 


CHAPTER   XV. 
SEWER   MAINTENANCE. 

ART.  83.     REQUIREMENTS  OF  PROPER  MAINTENANCE. 

THE  requirements  for  keeping  a  sewerage  system  in  good 
running  order  can  be  concisely  stated  as — preventing  and 
removing  deposits,  and  maintaining  ample  and  safe  ventila- 
tion. 

As  previously  stated,  the  main  dependence  for  preventing 
deposits  is  flushing.  If  a  deposit  remains  for  any  time  it  is 
apt  to  continually  increase  and  become  more  difficult  of 
removal,  and  deposits  should  therefore  be  removed  as  soon  as 
possible  after  forming.  This  the  automatic  flush-tank  is  sup- 
posed to  do  for  800  to  1000  feet  below  it,  but  any  forming 
below  this  limit  will  probably  need  to  be  removed  by  hand- 
flushing  from  a  manhole  or  by  the  use  of  special  appliances. 
If  deposits  continually  form  in  any  one  place  and  are  not 
apparently  occasioned  by  articles  which  should  not  be  intro- 
duced into  the  sewer  it  may  be  advisable  to  place  a  flush-tank 
at  the  head  of  where  such  deposits  form,  at  one  side  of  the 
sewer,  but  connected  with  it  at  a  manhole  or  by  a  Y  branch. 
If  obstructions  are  frequently  formed  at  any  one  place  by  the 
introduction  of  improper  matters,  such  as  ashes,  bones,  etc., 
the  source  of  these  should  be  ascertained  and  the  parties 
responsible  therefor  punished. 

It  should  not  be  taken  for  granted  that  a  sewer  is  working 
properly,  but  the  system  should  be  inspected  once  a  week  or 

347 


348  SEWERAGE. 

at  least  once  a  fortnight.  This  may  require  merely  a  look 
into  each  flush-tank  to  see  that  it  works  properly,  into  each 
inlet  or  catch-basin  to  see  that  it  is  clean  and  the  grating 
unobstructed,  and  into  each  manhole  (the  dirt-pan  being  at 
the  same  time  removed  and  emptied)  to  see  that  the  sewage 
is  flowing  with  sufficient  velocity  and  is  apparently  not 
dammed  back  by  any  deposit  below.  But  during  the  first 
few  months  of  his  service  the  inspector  should  enter  each 
manhole  and  look  through  the  sewer  at  each  inspection  until 
he  becomes  familiar  with  its  condition  of  depth  and  velocity 
of  flow  when  in  good  order.  If  there  are  any  considerable 
odors  observed  about  any  appurtenance  the  cause  should  be 
discovered  and  removed.  This  will  usually  be  a  large  deposit 
or  imperfect  ventilation,  except  in  the  case  of  catch-basins,, 
where  it  probably  means'improper  or  infrequent  cleaning. 

The  catch-basins  should  be  cleaned  after  every  rainfall. 
There  is  danger  of  putrefaction  and  objectionable  odor  from 
these  if  this  is  not  done  within  two  or  three  days  after  each 
rain,  but  this  is  almost  impracticable  in  large  cities,  where 
there  are  one  or  two  on  every  corner,  without  the  use  of  an 
enormous  number  of  men  and  carts,  since  each  cart  with  three 
men  will  clean  but  five  to  ten  catch-basins  a  day.  As  an 
example  of  what  is  usually  done  in  this  line,  a  large  city  in 
New  England,  which  is  considered  to  have  an  excellent 
Department  of  Public  Works,  during  the  entire  year  of  1890 
cleaned  its  noo  catch-basins  an  average  of  1.84  times  each. 
It  seems  almost  impossible  that  these  catch-basins  could  hold 
the  heavier  matter  washed  from  the  streets  during  six  or 
seven  months  (or  if  so  the  small  amount  contributed  by  each 
storm  would  have  done  little  harm  in  the  sewer),  and  the  infer- 
ence is  that  a  large  part  of  this  was  not  held,  but  was  washed 
into  the  sewer;  also  that  the  catch-basins  were  in  an  unsani- 
tary condition  a  large  part  of  the  time.  When  so  treated  they 
might  better  be  replaced  with  plain  inlets. 


SEWER   MAINTENANCE.  349 

A  record  should  be  kept  of  all  sewer-inspections,  each  line 
of  sewer  and  each  appurtenance  having  a  record  of  its  own 
showing  when  it  was  inspected,  its  condition,  when  cleaned, 
what  repairs  were  made  to  it,  with  their  nature  and  cost;  of 
the  frequency  of  flushing  or  of  the  discharge  of  each  automatic 
flush-tank;  of  the  location  and  date  of  making  each  house- 
connection,  with  all  details  as  to  route,  size,  and  grade  of 
connection-pipe,  cost,  by  whom  ordered,  by  whom  put  in  (if 
by  private  contractor). 

The  house-drainage  is  usually  supposed  to  be,  but  seldom 
is,  looked  after  by  the  owner.  It  is  exceedingly  desirable  to 
have  a  sanitary  inspection  made  of  every  house  by  a  city 
inspector  at  intervals  of  not  more  than  12  months;  but  such 
a  plan  would  hardly  be  favored  by  most  American  communi- 
ties, but  would  be  looked  upon  as  an  impertinence.  It  is  the 
city's  duty,  however,  to  insist  upon  all  owners  and  tenants 
observing  the  sanitary  regulations  as  to  construction  and  use 
of  house-drainage  systems. 

Extensions  of  the  system  should  of  course  be  made  with 
as  much  care  as  were  the  original  sewers,  and  no  alterations 
made  in  the  original  plans  without  a  careful  consideration  of 
their  effect  upon  the  system  as  a  whole. 

ART.  84.     FLUSHING. 

When  automatic  flush-tanks  are  used  they  should  be  in- 
spected at  intervals  to  insure  their  regular  discharging.  The 
most  common  failing  with  siphon-tanks  is  the  trickling  over 
of  the  water  into  the  sewer  as  fast  as  it  enters  the  tank  after 
it  has  once  reached  the  level  of  the  top  of  the  bend.  Under 
this  condition  the  siphon  will  never  flush.  This  trickling  may 
be  due  to  faulty  designing,  but  is  usually  caused  by  a  leaking 
joint  or  blow-hole  in  the  iron  siphon  at  some  point,  which 
must  be  corrected.  The  frequency  of  discharge  is  regulated 


35°  SEWERAGE. 

by  the  cock  admitting  the  water.  This  can  be  adjusted  only 
by  actual  trial  with  each  tank.  It  is  a  good  plan  to  have  one 
or  more  registering  reservoir-gauges  for  use  in  the  flush-tanks 
which  will  indicate  the  times  of  discharge.  A  simple  one, 
but  sufficient  for  this  purpose,  can  be  made  with  a  clock- 
works actuating  a  cylinder  on  which  the  height  of  water  is 
constantly  registered  by  a  pen  whose  motion  is  caused  by  the 
rise  and  fall  of  a  float,  the  pen  and  a  rod  from  the  float  being 
attached  to  opposite  ends  of  a  lever  with  unequal  arms,  so 
that  the  path  of  the  pen  is  but  4  or  5  inches  long.  Such  an 
apparatus  left  for  a  day  or  two  in  a  flush-tank  will  serve  in 
place  of  frequent  visits  to  it,  and  can  be  moved  from  one  to 
another  as  each  is  adjusted  to  the  desired  frequency  of  dis- 
charge. The  waste  of  water  caused  by  flushing  oftener  than 
once  in  eighteen  to  twenty-four  hours  is  not  justified  by  any 
proportionate  advantages. 

Reference  has  already  been  made  (Art.  47)  to  flushing 
directly  from  2-  or  4- inch  branches  led  from  the  water-main 
into  the  flush-tank.  In  using  these  the  valve  is  ordinarily 
opened  to  its  full  extent,  or  so  much  as  is  necessary  to  main- 
tain the  height  of  water  in  the  flush- tank  as  great  as  is  safe 
for  the  tank  or  sewer.  It  may  be  left  open  until  such  time 
as  the  water  flowing  through  the  manholes  below  is  perfectly 
clean.  It  will  be  necessary  to  use  the  most  solid  construction 
in  the  flush-tank  to  resist  the  considerable  force  with  which 
the  water  leaves  the  water-pipe. 

Instead  of  connecting  the  flush-tank  with  the  water-main 
by  a  large  pipe  a  small  one  is  sometimes  used,  and  the  tank 
filled  from  this  after  closing  the  sewer  end,  which  is  then 
opened  and  the  contained  water  allowed  to  flush  the  sewer. 
This  method  takes  much  longer  than  the  previous  one  and 
is  consequently  more  expensive.  In  some  cases  the  flush-tank 
is  filled  by  hose  from  the  nearest  fire-hydrant. 

In  some  cities  the  water  is  conveyed  to  the  flush-tanks  in 


SEWER   MAINTENANCE.  351 

carts,  and  either  the  tanks  filled  from  these  and  discharged  by 
hand  as  above,  or  from  the  bottom  of  the  cart  a  large  pipe  or 
canvas  hose  is  lowered  into  the  flush-tank  and  connected  with 
the  end  of  the  sewer,  into  which  the  water  is  discharged  under 
a  head  equal  to  the  elevation  of  the  cart  above  the  sewer. 
In  New  Haven,  Conn.,  such  a  cart  is  used  holding  700  gal- 
lons, in  connection  with  which  an  ovoid  ball  is  passed  down 
the  sewer  to  assist  in  the  cleansing,  its  distance  from  the 
flush-tank  being  regulated  by  an  attached  cord  which  passes 
up  through  the  sewer  and  flushing-pipe  to  the  surface.  These 
carts  are  ordinarily  used  at  manholes  along  the  line  of  the 
sewer  rather  than  at  flush-tanks  proper. 

Flushing,  as  has  been  stated,  is  seldom  effective  for  more 
than  800  to  1000  feet  below  the  point  of  entrance  of  the 
flushing-water.  Hence,  when  automatic  tanks  are  not  used 
at  the  head  of  every  section  of  such  length  which  requires 
flushing,  this  is  performed  at  manholes  wherever  necessary. 
For  this  purpose  outside  water  may  be  introduced  by  carts, 
as  just  described;  or  all  the  openings  in  a  manhole  may  be 
stopped  and  the  manhole  filled  by  hose,  when  the  plug  to  the 
down-stream  opening  is  removed  and  the  sewer  below 
flushed;  or  only  this  opening  is  closed,  and  the  sewage  is 
permitted  to  back  up  in  the  sewer  above,  when  the  plug  is  re- 
moved and  the  sewage  performs  the  flushing.  The  last  method 
is  not  particularly  satisfactory  with  pipe  sewers  in  most 
instances,  since  the  head  obtainable  is  usually  very  small  and 
the  velocity  of  flush  consequently  the  same,  and  if  the  house- 
connection  pipes  are  on  a  flat  grade  the  sewage  may  back  up 
these  to  an  undesirable  height.  Deposits  also  may  form  while 
the  sewage  is  accumulating,  which  will  not  be  removed  by  the 
flush  if  near  the  upper  end  of  the  dammed  sewage,  and  the 
time  required  for  a  sufficient  volume  of  sewage  to  collect  will 
often  be  considerable  and  increases  directly  as  the  necessity 
for  frequent  flushing  in  each  case. 


352  SEWERAGE. 

The  plugs  used  for  stopping  pipe  and  small  brick  sewers 
may  have  any  of  a  variety  of  forms.  One  design  is  a  simple 
conical  cork-shaped  piece  of  wood  with  heavy  rubber  so  fast- 
ened around  it  as  to  come  between  it  and  the  inside  of  the 
sewer  when  the  plug  is  pushed  into  place  and  make  a  water- 
tight joint.  Another  consists  of  a  solid  centre  of  plank, 
around  the  edge  of  which  is  placed  a  pneumatic  tube  similar 
to  a  bicycle-tire,  which  is  inserted  just  inside  the  sewer  and 
the  tire  inflated  by  a  bicycle-pump.  These  have  ropes 
attached  by  which  to  draw  them  out  of  the  sewer  when  the 
manhole  or  flush-tank  is  full,  the  air  being  first  released  from 
the  tube  of  the  one  last  described. 

Another  plan,  that  of  bracing  a  loose  frame  or  hinged  gate 
against  the  end  of  the  sewer  in  a  manhole,  is  hardly  applicable 
to  properly  constructed  systems,  where  the  manhole-channel 
and  sewer  are  continuous,  but  may  be  used  in  a  flush-tank 
designed  for  the  purpose.  The  cover,  whether  loose  or 
hinged,  may  be  held  in  place  by  a  brace  hinged  at  the  middle 
and  extending  from  the  cover  across  the  flush-tank  to  the 
opposite  wall.  A  rope  is  attached  to  the  hinge  of  the  brace 
and  by  pulling  this  when  the  tank  is  full  the  brace  folds  up 
and  releases  the  cover. 

In  large  sewers  it  is  generally  impracticable  and  unneces- 
sary to  dam  back  the  sewage  higher  than,  or  even  as  high  as, 
the  crown  of  the  sewer,  and  a  dam  one  half  or  two  thirds  the 
height  of  the  sewer  is  sufficient.  This  may  be  made  similar 
to  those  already  described,  but  not  filling  the  entire  bore  of 
the  sewer.  Or  a  "  pocket  dam  "  may  be  used.  This  con- 
sists of  a  bag  of  tarred  canvas  having  rings  around  its  mouth 
and  a  rope  passing  through  these  long  enough  to  reach 
from  the  sewer  to  the  surface.  Another  rope  is  fastened  to 
the  bottom  of  the  bag.  This  bag  is  filled  with  water  and 
placed  in  the  sewer-invert,  being  held  upright  by  the  rope 
through  the  rings,  and  serves  as  a  dam  to  the  sewage.  When 


SEWER   MAINTENANCE.  353 

this  has  raised  sufficiently  this  rope  is  released,  the  bag 
collapses  and  is  removed  by  the  rope  attached  to  its  bottom. 

In  very  large  sewers  flushing,  if  practised  at  all,  must 
generally  be  done  with  sewage,  on  account  of  the  enormous 
quantity  of  water  required  for  this  purpose.  But  this  prac- 
tice is  not  recommended  where  sufficient  water  can  be 
obtained.  In  the  case  of  storm  or  combined  sewers  advantage 
should  be  taken  of  light  rains  by  damming  up  the  run-off  from 
them  in  the  sewers  and  flushing  with  this  comparatively  clean 
water.  Heavy  storms  of  course  need  no  assistance  in  their 
flushing  effect. 

To  ascertain  the  height  to  which  water  in  a  large  sewer 
has  risen  in  flushing  (or  at  any  other  time,  as  during  storms) 
an  ingenious  method,  employed  at  Omaha,  Neb.,  is  to  drive 
into  the  wall,  2  inches  apart  vertically,  small  iron  rods  with 
the  ends  turned  up,  on  each  of  which  rests  a  cork  with  a  hole 
in  its  bottom,  which  can  be  readily  floated  off  when  reached 
by  the  water.  Upright  whitewashed  sticks  placed  in  the  ver- 
tical diameter  of  the  sewer  have  been  used  for  the  same 
purpose,  but  not  with. perfect  success. 

Of  the  above  methods  of  flushing  Andrew  Rosewater  con- 
siders the  automatic  flush-tank  the  least  expensive,  the  use 
of  4-inch  water-pipes  with  hand-valves  next,  then  the  use  of 
hose  from  the  hydrants,  and  the  water-cart  method  the  most 
expensive.  Cleaning  sewers  in  New  Haven  by  the  water-cart 
above  described  cost  $3  to  $4  per  mile  cleaned.  One  argu- 
ment in  favor  of  hand-flushing  is  that  it  renders  more  prob- 
able frequent  inspection  of  the  system,  which  will  be  made  at 
the  time  of  flushing;  but  on  the  other  hand  pressure  of  other 
duties  or  carelessness  may  cause  longer  intervals  between 
flushings  than  is  desirable.  As  a  general  rule  automatic 
tanks  should  be  used  on  pipe  sewers  where  there  is  not 
retained  by  the  city  a  constant  force  of  laborers  for  mainte- 
nance of  sewers  and  streets  and  similar  purposes.  In  the  case 


354  SEWERAGE. 

of  large  brick  sewers  it  is  probably  best  to  resort  to  one  of 
the  methods  of  hand-flushing.  For  pipe-sewer  dead-ends  in 
cities  with  a  maintenance  force  automatic  appliances  are 
desirable,  but  are  in  many  instances  not  used.  When  any 
flushing  is  done  elsewhere  than  at  dead-ends  hand-flushing  is 
generally  resorted  to. 

ART.  85.     CLEANING. 

The  purpose  of  flushing  is  to  prevent  deposits,  or  rather 
to  prevent  the  accumulation  and  solidifying  of  deposits.  But 
from  the  insufficiency  or  infrequency  of  flushing  this  object  is 
sometimes  not  attained;  or  obstinate  obstructions  may  be 
formed  by  sticks,  stones,  or  other  matter  which  flushing  is  not 
expected  to  remove,  and  these  must  be  removed  by  hand  or 
some  other  method.  Catch-basins  must  be  cleaned  by  hand, 
and  this  should  be  done  frequently.  The  manhole  dirt- 
buckets,  also,  should  be  cleaned  at  intervals.  These  last  are 
merely  removed  from  the  manholes  and  dumped  into  a  cart 
or  wheelbarrow. 

The  catch-basins  are  generally  cleaned  by  ordinary 
shovels,  the  dirt  being  taken  to  the  surface  by  a  bucket  and 
emptied  into  a  cart.  Two  men  and  a  cart  and  horse  suffice 
for  this  work.  In  some  cities,  and  especially  when  the  catch- 
basins  are  small,  the  dirt  is  removed  with  long-  and  heavy- 
handled  hoes,  the  blade  of  the  hoe  being  at  right  angles  to  the 
handle  and  about  8  by  10  inches  in  size.  These  are  used 
from  the  surface  through  the  manhole-opening  or  that  left  by 
removing  the  grating.  Catch-basin  walls  should  be  thoroughly 
cleaned  with  a  hose  and  broom  and  washed  with  a  solution  of 
chloride  of  lime  or  some  deodorizer,  but  this  is  seldom  done. 
The  cost  of  cleaning  a  catch-basin  will  vary  probably  from  50 
cents  to  $2  each,  depending  upon  their  size,  the  frequency  of 
cleaning,  and  other  special  circumstances  or  conditions;  $1.40 


SEWER  MAINTENANCE. 


355 


FIG.  34. — APPLIANCE  FOR 
CLEANING  SIPHON-SUMP. 


seems  to  be  about  the  average  for  large  cities.  Catch-basins 
at  the  ends  of  siphons  are  difficult  to  clean,  being  in  most 
cases  at  the  bottom  of  a  shaft  containing  many  feet  of  water. 
Long-handled  hoes  may  be  used,  or  the  siphon  may  be  closed 
and  emptied  of  sewage  to  permit  reaching  the  catch-basin. 
An  apparatus  acting  on  the  principle  of  the  steam-siphon  01 
sand-pump  is  used  with  success  in  the  Waltham,  Mass., 
siphon,  emptying  the  catch-basin  or  sump  without  the  siphon 
being  emptied.  The  pipe  B,  Fig. 
34,  is  lowered  into  the  sump  and 
the  nozzle  is  attached  to  a  hose 
from  a  hydrant.  When  the  water 
is  turned  on  the  sand  and  other 
solid  material,  mixed  with  sewage, 
is  sucked  up  through  B  and  dis- 
charged through  A  into  the  sewer, 
from  which  it  is  prevented  from 
returning  by  a  temporary  dam  in  the  end  of  the  sewer. 

Small  sewers  are  cleaned  by  flushing  when  this  is  possible, 
but  in  many  cases  other  means  must  be  resorted  to.  The 
use  of  "  pills  "  is  convenient  where  there  are  no  stones,  sticks, 
or  other  hard  materials  in  the  sewer.  These  are  round  balls, 
usually  of  wood,  which  are  floated  through  the  sewer  either 
in  the  sewage  or,  if  there  is  not  enough  of  this,  by  flushing 
water.  A  set  of  these  2,  3,  4,  5,  7,  9,  etc.,  inches  in  diameter 
should  be  kept  on  hand.  When  a  sewer  is  to  be  cleaned  the 
smallest  pill  is  floated  through  from  one  manhole  to  the  next, 
where  it  is  caught  by  an  assistant;  the  others  are  then  sent 
through  in  the  order  of  their  sizes  until  all  have  passed 
through  up  to  the  size  one  inch  smaller  than  the  sewer. 
When  any  ball  reaches  a  point  where  the  opening  is  contracted 
by  sediment  to  less  than  its  diameter  the  ball,  which  has 
floated  and  rolled  along  the  top  of  the  sewer,  dams  up  the 
water  until  it  has  sufficient  head  to  force  its  way  under  the 


SEWERAGE. 

ball  and  scour  out  the  sediment.  The  ball  rolls  slowly  ahead, 
the  current  washing  away  the  sediment  for  an  inch  or  two 
under  it.  If  there  is  a  lamp-hole  on  the  line  the  ball  may 
bob  up  into  it,  and  a  man  should  be  stationed  there  with  a 
pole  to  push  the  ball  down  and  into  the  sewer  below  the 
lamp-hole.  If  a  stone  or  stick  is  among  the  deposit  the  ball 
may  be  stopped  by  it,  in  which  case  both  stone  and  ball  must 
ibe  removed  by  another  method.  The  pill  cannot  be  used 
•when  the  sewer  is  stopped  entirely  so  that  there  is  no  flow 
through  it.  No  cord  should  be  fastened  to  any  of  these 
round  balls,  as  it  is  liable  to  be  rolled  about  them  and  wedge 
them  in  the  sewer,  catch  in  obstructions,  and  generally  give 
trouble.  Ovoid  balls,  however,  are  sometimes  used  with 
cords  attached.  These  do  not  roll  along  the  top  of  the  sewer, 
and  may  need  to  be  weighted  to  prevent  the  friction  between 
them  and  the  sewer  top  interfering  with  their  motion  ahead. 
4  In  place  of  the  pill,  particularly  in  sewers  larger  than  12 
or  1 5  inches,  a  small  carriage  is  sometimes  used  which  travels 
on  wheels  through  the  sewer,  its  front  being  of  such  a  shape 
as  to  almost  fill  its  bore  except  for  an  inch  or  two  at  the 
bottom.  Where  the  sewer  is  not  more  than  3  or  4  feet  in 
diameter  the  carriage  is  usually  provided  with  other  wheels 
on  top,  which  are  pressed  against  the  sewer-arch  by  springs. 
This  contrivance  is  hauled  through  the  sewer  by  a  rope,  which 
has  first  been  introduced  into  it  by  floating  through  the  sewer, 
a  piece  of  wood  or  cork  carrying  a  cord  to  the  end  of  which 
the  rope  is  attached.  Another  rope  is  fastened  to  the  rear  of 
the  carriage  to  haul  it  back  if  it  strikes  an  immovable  obstruc- 
tion. This  is  a  modification,  and  on  a  small  scale,  of  the 
method  employed  for  cleaning  the  Paris  sewers,  where  a  plank 
form,  similar  in  shape  to  and  but  little  smaller  than  the  sewer- 
invert,  is  carried  by  a  boat  or  wagon  and  lowered  into  the 
sewer  as  far  as  necessary  to  cause  a  scouring  of  the  deposit. 
The  boat  or  car  is  carried  forward  by  the  water  backed  up 


SEWER   MAINTENANCE.  357 

behind  the  scouring-form,  which  is  raised  or  lowered  to  the 
proper  position  by  a  workman  riding  in  the  conveyance. 

These  methods  all  depend  upon  the  scouring  action  of  the 
water  and  presuppose  a  passage  through  the  sewer.  Other 
contrivances  for  cleaning  a  small  sewer  under  such  circum- 


FIG.  35. — DISK  FOR  CLEANING  SEWERS. 

stances  are  based  upon  the  use  of  main  strength  to  haul  the 
material  out.  Probably  the  simplest  is  in  the  shape  of  a 
heavy  plank  disk  to  which  a  rope  is  attached  by  three  short 
light  chains  fastened  to  as  many  bolts  through  the  disk.  One 
of  these  chains  is  attached  at  each  side  and  one  at  the  bottom 
of  the  disk,  and  their  relative  lengths  are  so  arranged  that 
when  all  are  taut  the  top  of  the  disk  will  incline  a  little  away 
from  the  rope.  Upon  the  other  side  of  the  disk,  at  its  top, 
is  fastened  another  rope.  By  the  latter  it  is  pulled  a  short 
distance  into  the  sewer,  lying  flat;  the  other  rope  is  then 
pulled,  when  the  disk  rises  into  an  upright  position  and  scrapes 
along  the  deposit  in  front  of  it.  It  is  well  not  to  draw  this 
too  far  into  the  sewer  at  once,  but  to  clean  only  a  few  feet  at 
each  trip.  The  dirt  can  be  scraped  to  a  manhole  and  there 
removed  by  buckets.  It  is  awkward  pulling  in  a  manhole 
bottom,  and  it  is  well  to  arrange  a  pulley  in  a  frame,  around 
which  the  rope  passes,  as  also  around  another  pulley  at  the  top 
to  permit  of  a  horizontal  pull.  The  lower  frame  may  consist 
of  two  4  X  6  or  4  X  8  timbers  fastened  to  each  other  parallel 
and  a  short  distance  apart,  between  which  the  pulley  turns  in 
journals  fastened  to  their  under  sides,  these  timbers  being 
braced  against  the  inside  arch  of  the  sewer  and  the  pulley 
being  in  the  centre  of  the  manhole  (see  Fig.  36).  This 
method  can  be  used  where  the  material  is  too  heavy  to  be 


358 


SEWERAGE. 


scoured  out  by  pills  or  similar  contrivances,   and  also  as  a 
substitute  for  these. 

In  some  cases  the  sewer  will  be  found  entirely  stopped,  so 
that  no  cord  can  be  got  through  it,  and  an  opening  must  be 
forced  through.  A  rod  of  some  kind  is  used  for  this  purpose. 
Since  none  longer  than  5  feet  can  be  got  into  the  sewer 
through  the  manhole  (unless  it  be  too  flexible  for  efficient 
service)  rods  of  this  length  made  to  joint  together  are  gen- 


fe,y<<<^<</<<<^^^ 

\\^^Y^N\V^\Y^\x<^\^\<::9c^x^W^ 

FIG.  36. — METHOD  OF  USING  CLEANING-DISK. 

erally  used.  These  are  sometimes  lengths  of  gas-pipe  with 
screw-couplings,  or  in  some  cities  I-  to  ij-inch  maple  rods 
with  brass  screw-caps  fastened  to  their  ends  are  used. 
These  are  forced  through  the  obstruction  by  working  them 
back  and  forth  or  even  by  driving  with  a  hammer.  When  an 
opening  is  once  made  it  is  well  to  leave  the  rod  in  it  and 
work  it  a  little  back  and  forth  as  the  sewage  flows  through 
until  the  hole  is  too  large  to  be  in  danger  of  immediately 
stopping  again,  when  a  pill  or  cord  may  be  floated  through 
and  the  cleaning  completed  by  one  of  the  above  methods. 

A  small  sewer  or  sub-drain  may  also  be  cleaned  by  the  use 
of  hose,  as  explained  in  Art.  78. 

In  some  cases  the  obstruction  may  be  so  obstinate  as  to 
necessitate  the  digging  up  of  the  sewer.  Before  doing  this 
its  exact  location  should  be  ascertained  by  pushing  a  rod  to  it 


SEWER   MAINTENANCE.  359 

through  the  sewer  and  measuring  its  length,  or  by  the  use  of 
mirrors,  as  previously  described. 

For  cleaning  house-connections,  sub-drains,  and  other 
small  pipe  which  cannot  be  readily  reached  the  hose  is 
excellent,  sufficient  water  being  turned  through  it  to  make  it 
stiff  enough  to  be  pushed  through  the  pipe;  or  rods  may  be 
used,  as  for  the  larger  sewers.  Instead  of  a  rod  the  city  of 
Waltham,  Mass.,  has  used  for  these  cases  a  length  of  steam- 
hose  filled  with  sand,  a  wooden  plug  being  fastened  in  the 
end  of  it.  This  is  flexible,  but  stiff  enough  for  use  in  a  pipe 
only  3  to  5  inches  in  diameter. 

Even  pipe  sewers  of  18  inches  diameter  and  up  can  be 
entered  for  inspection  and  cleaning  by  hand.  It  is  reported 
that  in  Waltham  a  Hungarian  crawled  through  850  feet  of 
1 5 -inch  pipe  running  2^-  to  4  inches  deep  with  sewage,  there 
being  in  at  least  one  place  not  over  9  inches  of  clear  space 
above  the  deposits  and  sewage.  The  author  has  seen  a  con- 
tractor crawl  through  200  feet  of  1 8-inch  sewer,  and  it  is 
nothing  unusual  for  a  man  to  pass  through  almost  any  length 
of  24-inch  pipe.  A  large  stone  or  a  stick  wedged  across  the 
sewer  can  frequently  be  removed  in  this  way  and  the  necessity 
for  digging  up  the  pipe  avoided. 

If  the  sewer  is  found  to  be  broken  in  any  place  there  is 
generally  but  one  thing  to  do,  to  dig  down  to  and  replace  it. 
A  sewer  which  is  only  cracked  or  is  leaking  badly  has  been 
repaired  by  inserting  inside  of  it  a  line  of  screw-joint  pipe  as 
large  as  can  be  slipped  into  it,  and  sealing  the  space  between 
the  two  at  the  ends  with  cement.  The  substitution  of  new 
pipe  would  probably  be  cheaper  in  most  cases,  however. 

When  small  pipe  is  only  coated  or  contains  but  little 
deposit  it  is  sometimes  cleaned  by  the  use  of  a  wire  brush,  just 
the  size  of  the  sewer,  fixed  upon  the  end  of  a  rod  similar  to 
those  already  described. 

The  cleaning  of  sewers  large  enough  to  permit  a  man  to 


360  SEWERAGE. 

work  in  them  needs  no  special  discussion.  If  they  are  large 
enough  the  dirt  may  be  carried  to  the  manhole  in  a  low  car 
running  on  the  sewer  bottom.  In  smaller  sewers  it  may  be 
shovelled  or  hoed  into  a  pile  at  each  of  two  manholes  from  a 
point  midway  between  them  and  removed  in  buckets. 

An  inverted  siphon  may  be  cleaned  as  an  ordinary  sewer, 
after  the  sewage  flow  has  been  diverted  to  the  other  siphon- 
pipe  or  dammed  up  and  the  sewage  contained  in  it  pumped 
out. 

In  1891  the  cleaning  of  123  miles  of  sewers  in  St.  Paul 
cost  $6208,  or  about  $50  per  mile;  labor  20  cents  and  team 
and  driver  30  cents  per  hour,  foreman  $4.18  daily.  The  cost 
of  removing  stoppages  from  small  sewers  will  probably  aver- 
age about  $2  or  $3  each.  The  annual  cost  per  mile  of  keep- 
ing a  system  of  pipe  sewers  clean  probably  varies  between  $10 
and  $75  in  most  cases;  it  should  not  exceed  $10  to  $25  for  a 
well-designed  and  -constructed  system  containing  20  miles  or 
more  of  sewers,  with  intelligent,  economic  maintenance,  and 
during  some  years  no  expense  for  this  purpose  may  be 
required. 


INDEX. 


Acceptance  of  a  system,  Requirements  for 215 

Adams  Sewage-lift 152 

Advertising  contracts 239 

Air,  sewer,  Character  of 96,  99 

Alignment,  Giving  trench 244 

Alleys,  Sewers  in 1 18 

Angles  and  bends  in  sewers 72,  119 

Arches,  Providing  for  thrust  of 298,  308 

Assessments,  Conditions  governing 233,  236 

,  Methods  of  making 231 

Atlantic  City,  Gaugings  of  sewage  flow  at 39 

Back-filling,  Cost  of  tamping 212 

"        "     ,  Laborers  used  for 268 

"     ,  Specifications  for 212 

Barrel,  sewer,  Shape  of 81,  158 

Beginning  construction,  Points  for 241 

Bends  in  sewer  lines 72,  1 19 

Benefits  derived  from  sewerage I,  2,  18,  139,  236 

Berlier  system  of  sewerage 7 

Bids,  Receiving  and  considering .'  239 

Blacksmith,  Necessity  for,  during  construction 266 

Borings,  Test,  along  sewer  lines 109 

Boulders,  Removing,   from  trench 274 

Braces,  Extensible 287 

,  Measuring  trench  for 287 

Branches,  Laying  sewer 209,  242,  251,  296,  341 

Brick  for  sewers,  Cost  of 227 

"        "     ,  Specifications  for 195 

Brick  sewers,  Abrasion  of 77 

"      ,  Centre  for 300- 

"      ,  Cost  of  construction 230 

in  quicksand 322 

"       ,  Invert  backing  for 297,  304 

"      ,  Method  of  building 299,  316 

"         "      ,  Templet  for 248,  298 

361 


362  INDEX. 

PAGE 

Bridging  trenches,  Specifications  for 201 

Burlington,  Vt.,  Gaugings  of  sewage  flow  at 40 

C,  Effect  of  variations  in  R  upon 62,  71 

",  Meaning  of 61 

",  value  of,  Formulas  for  the 62 

Canals,  Crossing  under 337 

Capacity,  Designing  for  future 113 

Catch-basins,   Cleaning 147,  347,  354 

,  Construction  of 181 

"        "      ,  Where  to  use 146,  347 

Caving  of  banks,  Avoiding 273,  279 

Cement,  Cost  of 231 

pipe  joints,  Cost  of 228 

sewer-pipe,  Use  of 158,  170 

"   ,  Specifications  for 194 

"       ,  Specifications  for 197 

Centre  for  brick  sewers 302 

Cesspools 3 

Chemical  precipitation 26 

Chezy  formula , .- 61 

Circular  sewers,  Conditions  favoring  use  of 81 

Cleaning  large  sewers 356,  360 

sewers,  Cost  of 360 

small  sewers 264,  326,  355 

up  streets,  Specifications  for 215 

Coffer-dams,  Construction  of 332 

Combined  system  defined 9 

"       vs.  separate 10 

Concrete  sewers 163 

"      ,  Method  of  constructing 304 

"      ,  Specifications  for 203 

Consumption  of  water,  Daily  and  hourly  variation  in 33 

"      "     ,  Estimating  future 33 

"      "        per  capita,  Table  of 32 

Contract,  Form  of 223 

Contracting  work,  Advantages  and  disadvantages  of 237 

Contractor,  Duties  of 220 

Contracts,  Advertising 239 

"      ,  Awarding 240 

Cost,  Relative,  of  sewers  of  different  capacities 57 

"    .  See  material  or  work  in  question. 

Cremation  of  sewage 28 

Cross-section  of  sewer,  Effect  of  shape  of,  upon  velocity 69,  8 1 

Curves,  Loss  of  head  in 72 

Cutting  sewer-pipe 297 

Dead-ends  in  sewers 119 

Defective  sewers,  Contractor's  responsibility  for 215,  217 


INDEX.  363 

,  PAGE 

Delays  of  construction,  Provision  in  contract  for 217 

Depth  of  sewage,  Minimum  permissible 77,  83 

"    sewer  desirable 132,  148 

"      "        "    ,  Relation  of  Q,  S,  and  d  to ' 131 

Design,  Data  necessary  for  the 103,  106 

"      ,  Principles  of  sewerage 1 1 1,  136 

Des  Moines,  Gauging  of  sewage  flow  at 41 

Dilution,  Amount  of,  necessary  for  discharge  into  streams 24,  114 

"      ,  Disposal  by 20 

"  ,  Conditions  affecting 24,  28,  1 14 

"        in  tidal  waters,  Requirements  for 25,  108,  114,  334 

"      ,  Purification  by 21 

Discharge  into  rivers  and  tidal  waters.    See  Dilution. 

through  circular  sewers,  Effect  of  depth  upon 69 

"        egg-shaped  sewers,  Effect  of  depth  upon 70 

sewers,  Table  of 64 

partly  full,  Calculating  the 71 

Disk  for  cleaning  small  sewers 357 

Disposal,  Aims  of 16 

"       ,  Commercial  aspect  of 17 

defined 14 

,  Laws  affecting 12,  16,  19,  20,  24 

"       ,  Principles  involved  in 18 

"       ,  Treatises  on 14 

Drainage  area,  Ascertaining  size  of 103,  106 

"    ,  Data  necessary  concerning 104 

"        districts 117 

"        of  wet  soils 139,  315,  317 

Draining  Trenches.    See  Water,  Ground. 

Driving-cap  for  sheathing 285 

Dry-sewage  methods 2 

Dwelling,  Average  number  of  persons  in  a 35 

Earth-closet  system 5 

Earth,  Sewage  treatment  by  use  of 27 

Egg-shaped  sewers,  Proportional  dimensions  of 83 

"      ,  Advantages  of,  over  circular 83 

Engineer,  Power  of,  in  contract  work 220 

Engineer's  duties  before  construction , 241 

"       during  254 

Estimate  of  cost,  Data  for  making 226 

Excavated  materials,  Classification  of 198 

"       ,  Placing  of,  on  streets • 270 

Excavating  deep  trenches 271,  279 

machinery,  Advantages  of  using 199,  249,  275,  290,  336 

"  "        ,  Different  kinds  of 276 

"  "        ,  Economy  of 278 

"          trenches  by  hand 270 


364  INDEX. 


Excavating  trenches,  Cost  of 229,  315 

"       ,  Specifications  for 198 

Extra  work,  Specifications  for 218 

Factories,  Amount  of  sewage  from 35 

Family,  Average  number  of  persons  in  a 35 

Field-book,  Form  of  notes  in 250,  259 

Filtration,  Treatment  by 27 

Final  estimate  book,  Method  of  keeping 257 

"       ,  Definition  of 256 

"       ,  Preparing 260 

"    inspection 215,  260 

Fire,  Treatment  by 28 

Fish,  Effect  of  sewage  upon 21 

Flat-bottom  sewers 161 

Floats,  Use  of 108 

Flow  in  sewers,  Theory  of 60 

Flushing,  Appliances  for 93,  179,  349 

by  hand,  Methods  of 91,  350 

"  "       "  ",  Relative  cost  of  different 353 

"       "      vs.  automatic  flushing 353 

"    roof-water 92 

"       ,  Efficiency  of 90 

from  streams  and  tide-waters 92 

"     water-mains   direct 95,  350 

"       ,  Intervals  between 86 

,  Necessity  for 85,97,347 

"       ,  Proper  methods  of 88 

"       ,  Sea-water  for 93 

"       ,  Separate  sewers  without 90 

water,  Amount  of,  necessary 87 

Flush-tanks,  Amount  of  water  from 37,  94 

"        "     ,  Automatic  apparatus  for 93,  179,  349 

"        "     ,  Construction   of 178,  211,  308,  350 

"        "     ,  Inspection  of 349 

"     ,  Locating 145,  347 

"        "     ,  Method  of  building 308 

"         "      ,  Specifications  for 211 

"        "      ,  Testing   261 

Foremen,  Number  and  character  of 266 

Foundations,  Forms  of . .  298,  309 

,  Materials  for 310 

"      .   ,  Specifications  for 202 

,  Where  needed 189 

Gangs,  labor,  Size  and  number  of 265,  267 

Gorged  sewers,  Relieving 153,  185 

Grade  cord,  Setting  and  using 245,  246 

"      rod,  Form  and  use  of 248 


INDEX.  365 

PAGE 

Grade  stakes,  Use  of 245,  250 

Grades  of  combined  sewers 76 

"      "  house-sewers 75»  I34 

"      "  sewers,    Calculating 134 

,  Desirable 134 

"      "       "      ,  Maximum 77 

"      "  storm-sewers    76,  134 

Ground-water.    See  Water,  Ground. 

Hose  for  cleaning  small  sewers 264,  326 

House-connections,  Capacity  of  four-inch 342 

"  ,  Interference  of  storm-sewers  with 137 

,  Junction  of,  with  sewers 142 

"  "          ,  Line  and  grade  of 142 

"  "          ,  Locating   242, 251 

"  "          ,  Method  of  cleaning 359 

,  Necessity  of  careful  construction  of . . .   100,  141,  340 

,  Regulations  for 341,  346,  349 

,  Sewer  air  in 96 

,  Size  of 79,  342 

,  Ventilating  sewers  through 100,  344 

with  deep  sewers 188 

"      sewage,  Amount  of 31,  113,  120 

"  "    ,  Gaugings  of 37 

Hydraulic  radius,  Definition  of 61 

"     ,  Formula  for,  in  circular  sewers 75 

"     ,  Tables   of 69 

Ice,  Danger  in  sewage-polluted 24 

Imperfect  work,  Contractor  to  repair 217 

Imperviousness  of  ground  and  run-off 51,  124 

"        "     ,  Determining   124 

Incineration,  Treatment  by 28 

Injuries,  Responsibility  of  contractor  for 217 

Inlet  connections 143,  181 

,  Ventilating  sewers  through 100 

Inlets,  Construction  of 180,  308 

"      ,   Locating 112,145 

"     ,  Specifications  for 211 

Inspecting  sewers 260 

Inspection-hole 342 

Inspection  of  house-drainage 346,  349 

"    sewers,  Necessity  for 252,  347 

Inspector,  Duties  of 252,  255 

Intersections  of  sewers 165,  215 

Intercepting-sewers   1 16,  153 

Interceptors 154 

,  Leaping  weir 183 

,  Diverting    183 


366  INDEX. 

PAGE 

Invert  backing 297,  304 

"      blocks  163 

"    ,  Definition  of 245 

"      former  for  small  sewers 263 

Inverted  siphons,  Construction  of 186 

"      ,  Principles  of  design  of 138,  185 

"      ,  Where  used 81,  132,  251,  329 

Inverts  for  brick  sewers 164 

Iron  castings,  Specifications  for 195 

"  ,  wrought,  "  196 

Irrigation,  Disposal  by 27 

Joint  packing,  Specifications  for 197 

Joints,  Pipe  sewer 1 18,  168,  204,  319,  329 

,  Concrete  around 295,  319 

"    ,  Ward  flexible,  Cost  of  laying 334 

Kalamazoo,  Gaugings  of  sewage  flow  at 40 

Kuichling's  laws  of  run-off 48 

Kutter's  formula 62 

Laborers,  Housing  non-resident 269 

Lamp-holes,  Construction  of 178 

"        "    ,  Where  used 145,251 

Laying  sewer-pipe,  Cost  of 229 

"        "    ,  Specifications  for „ 206 

Leaks  in  sewers,  Stopping 206,  261,  319 

Levelling  necessary  for  designing 105,  107,  242 

Liernur  system  of  sewerage 7 

Lifting  sewage,  Methods  and  apparatus  for 149,  150 

"      ,  When  necessary 148 

stations,  Location  of 152 

"       ,  Number  of,  desirable 150 

Lines,  Locating  sewer 117,  244 

Manhole  bottoms 176,  306 

buckets    178 

steps 172,  307 

tops 177,  249,  307 

walls 177,  306 

Manholes,  Building,  in  quicksand 327 

"         ,  Cost  of 230 

"         ,  Crossing 174 

,  Dimensions  of 172 

,  Drop 174 

,  Location   of 144,  171,  336 

"         ,  Materials  and  shapes  of 306 

,  Method  of  building 306 

"  on  large  sewers 1 76 

"         ,  Purposes   of TOO,  144 

,  Shallow    172,308 


INDEX. 


Manholes,  Specifications  for 210 

,  Sub-drain  i?4,  3^7 

Map  required  for  designing 103,  107 

Masonry,  brick,  Specifications  for 205 

sewers,  Materials  and  shapes  of . 297 

"       ,  stone  block,  Specifications  for 206 

stone,  Specifications  for 204 

work  in  winter 296,  308 

Masons,  Number  of,  required 267 

Materials  of  sewer  construction.    (See  also  material  or  appurtenances 

in  question.) I57>  161 

Maul  for  driving  sheathing 285 

Measurement  of  work 220,  256 

Memphis,  Gaugings  of  sewage  flow  at 40 

Mirrors  for  inspecting  sewers 262 

Monthly  estimates,  Preparing 258 

Mortar,  Method  of  making 204,  300 

and  brick,  Handling 300 

n  in  Kutter's  formula,  Values  for 63 

Notes  of  the  work 250,  255,  257,  258 

"  Nuisance  "   defined 19 

Obj ect  of  a  sewerage  system 30 

Obstructions,  Causes  of,  in  sewers 85 

,  Passing,  by  siphon 251 

Office  buildings,  Amount  of  sewage  from 35 

Old  sewers,  Using,  in  new  system 155 

Outlet,  Deer  Island,  Cost  of 333 

Outlets  for  sewerage  systems 20,  105,  108,  133,  148,  153,  334 

"     ,  Construction  of 333 

Overflows  185 

Oysters,  Typhoid  fever  germs  in 21 

Packing,  joint,  Specifications  for 197 

Pail  for  earth-closet  or  pail  system 5 

Pail  system 4,  27 

Paving,  restoring,  Specifications  for 214 

Payments,  Times  of  making 223,  269 

Picks  273 

Piles,  Methods  of  driving 309 

Pills,  Use  of,  in  cleaning  sewers 264,  355 

Pipe,  broken,  Replacing,  in  sewers 341,  359 

"    ,  cement,  Specifications  for 194 

"    ,        "          vs.  vitrified  clay 170 

"    ,  drain,  Specifications  for 194 

"    ,      "    ,  Cost  of 228 

"    ,  heavy,  Methods  of  laying 292 

"    ,  House-drain   345 

"    ,  iron,  Cost  of .  228 


368  INDEX. 

PAGE 

Pipe  layers,  Number  of,  required 267 

"    ,  sewer,  Cutting 297 

"    ,       "     ,  Price    of 227 

"    ,      "    ,  Strength  of 167 

"    ,      "    ,  Thickness  of 166 

"      sewers,  Cleaning 264,  325,  355 

"  "     ,  Cost  of  laying 229 

"     ,  Imperfections  common  in 263 

"  "        in  quicksand 322 

"  "         "  wet  trenches 318,  325 

"  "     ,  Inspecting  254, 262 

"     ,  Laying,  up  or  down  hill 291,  317 

"  "     ,  Methods  of  laying 291,  319 

"     ,  Specifications  for  laying 206 

"    ,  two-foot  vs.  three-foot  lengths 170 

"    ,  vitrified,  Specifications  for 192 

Pipes  and  conduits,  Interference  with,  by  contractor 200 

"    ,  Water,  gas,  or  drain,  in  the  trench 274 

Plans,  sewerage,  Data  required  for 103 

Platforms  in  deep  trenches 271 

Plumbing,  Regulations  for  sanitary 341 

Pneumatic  systems 7 

Population,  Distribution  of,  in  families  and  dwellings 34 

"       ,  Districts  based  on  density  of 36,  116 

"       ,  Estimating  future  increase  in 35>  J  J3 

per  acre,  Rule  for  calculating 36 

Private  property,  Sewers  on 120 

Privies   2 

Profiles,  Information  to  be  shown  on 131,  137 

"        necessary   105 

"     ,  Preparing 107,  131 

Providence,  Gaugings  of  sewage  flow  at 38 

Pumping,  hand,  Methods  of 3".  3*6 

,  steam,         "          " 312 

"        .  See  Lifting. 

Pumps,  Hand,  on  construction  work 311 

"      ,  Steam,  on  construction  work 312 

"     ,  sewage,  Capacity  of,  necessary 149 

"      ,        "         Kinds  of,  in  use 151 

Quicksand,  Building  brick  sewers  in 249,  322 

"      ,  manholes  in 327 

"      ,          "         pipe  sewers  in 249,  322 

"      ,  Detecting  presence  of 1 10 

"      ,  Handling  trenches  in 268,  317,  320,  322 

"      ,  Qualities  of 320 

"      ,  Removing,  from  pipe  sewers 325 

"      ,  Sheathing   in 281,283,321 


INDEX.  369 


R.     See  Hydraulic  radius. 

Raceways,  Method  of  crossing  under 337 

Railroad  crossings,  Construction  at 335 

"  "        ,  Specifications  for c « 200 

Railroads,  Sewers  near 336 

Rainfall,  Rates  of,  in  various  sections 45,  123 

Ransome  method  of  building  sewers 305 

Relief  sewer,  Purposes  of 185 

Removing  a  pipe  from  a  sewer 341 

Rivers,  Methods  of  crossing 328 

"    ,  Discharging  sewage  into.    See  Dilution. 

Rock,  Determining  presence  of 109 

"       excavation,  Cost  of 229 

,  Measuring  257 

,  Sewers   in 189 

"  "         ,  Specifications  for 201 

Rods  for  cleaning  small  sewers 358 

Run-off  at  Nagpoor  reservoir 51 

"       "    Washington,  D.  C 48 

"      ,  Comparison  of  formulas  for 55 

conducted  through  gutters 59,  1 12 

"      ,  Diagrams  for  calculating 47 

"      ,  Factors   of 44 

"      ,  Formulas  for 52 

"      ,  ",  Discussion  of 54 

"      ,  Gaugings  of,  at  New  Orleans 47 

,  Kuichling's  laws  of 48 

"      ,  Method  of  calculating 124 

"      ,  Roe's  table  for 54 

S,  Definition  of 61 

St.  Louis,  Gaugings  of  sewage  flow  at 40 

Sand,  Cost  of 231 

"       for  mortar,  Specifications  for 196 

Sanitary  sewerage,  Requirements  of I 

Schenectady,  Gaugings  of  sewage  flow  at 39 

Sections  of  sewers 158 

Separate  system  vs.  combined 10 

"       defined  9 

Septic  tank  treatment 27 

Sewage,  Causes  of  danger  from 3,  1 8,  23,  25,  96 

"     ,  Composition   of 15,  31 

"        defined 15 

"     ,  Value  of 17 

"     .  See  House-  or  Storm-sewage. 

Sewerage,  Arguments  in  favor  of I,  2,  18,  139,  236 

Sewer-pipe.     See  Pipe,  Sewer. 

Shape  of  sewer  section 81,  158 


370  INDEX. 

PAGE 

Sheathers,  Number  of,  necessary 266,  268 

Sheathing,  Driving-cap  and  maul  for 282,  285 

,  Horizontal   281,  285 

"        ,  Materials  and  dimensions  of 284,  286 

,  Removing  289 

,    "        ,  Skeleton    280,  286 

"  trenches,  Cost  of 229 

,  Methods    of 280,287,321 

"  on  steep  slopes »  337 

"  "       ,  Specifications  for 200 

"  "        ,  When  necessary 273,  279 

,  When  to  be  left  in 288 

Shone  Ejectors •. 7,  152 

Shoring  buildings 200,  290 

Shovels    273 

Sidewalks,  Sewers  under 1 18 

Silt-basins,  Use  and  construction  of 182 

Siphons,  Inverted.    See  Inverted  siphons. 

Sizes  of  house  sewers,  Method  of  determining 31,  75,  78,  120 

"      "      "  "      ,  Minimum 79 

"      ,  sewers,  Calculating,  from  sewage  volume 120,  134 

"      "  storm  sewers,  Method  of  determining 44,  75,  122 

"      "        "  "      ,  Minimum 80 

Specifications,  Classification  of 190 

"          ,  Definition  of 190 

,  Requirements  of 191 

"          .  See  the  material  or  work  in  question. 

Staging  in  trenches,  Construction  of •. .  271 

Steep  slopes,  Sheathing  trenches  on 337 

Stone,  masonry,  Specifications  for 195 

"     ,  paving,  '   195 

Stoneware  sewer-pipe.    See  Pipe,  Vitrified. 

Stores,  Amount  of  sewage  from 35 

Storm  overflows 154 

"      sewage,  Data  for  determining  volume  of 122 

"      sewerage,  Extent  of 112 

"      sewer,  Determining  size  of 57,  66,  80,  134 

"      water,  Amount  of,  to  be  provided  for 56,  58 

Storms,  Damage  done  by 57 

"    ,  First,  second,  and  third  class 56 

Street  surfaces,  Breaking,  for  trenches 270 

"        ,  restoring,  Specifications  for 214 

Sub-drain  pipe,  Specifications  for -. 194 

Sub-drains,   Cleaning 325 

"        "       ,  Construction  of 187 

for  handling   ground-water 312,317,318 

in    quicksand 324,  325 


INDEX.  371 

PAGE 

Sub-drains,  Inspecting 264 

"        "       ,  Specifications  for 209 

"        "      ,  Necessity  for 139 

"        "      ,  Outlets  for 140 

"        "      ,  Size  of 141 

Sub-invert  spaces 189 

Surveys  necessary  for  designing 106 

System  of  sewerage,  Which,  to  adopt 12,  115,  149 

Tamping  trenches,  Cost  of 212 

"       ,  Methods  of 213,  295,  297 

"        ,  Specifications  for 213 

Templet  for  sewers 298 

,  Inspector's   or  skeleton 262 

Tidal   reservoirs 148 

Timber,  Specifications  for 197 

Time-keeper,   Duties   of 266 

Toronto,  Gaugings  of  sewage  flow  at 39 

Traps,  Location  and  use  of 97,  182,  343 

Treatment,  Sewage,  defined 14 

"       ,  Difficulty   of 15 

"      ,  Method  of,  to  be  adopted 115 

,  Methods  of 26 

Trench  machine.     See  Excavating  machine. 

Trench,  Storm-  and  house-sewer  in  the  same 120 

Trenches,    Excavating 270 

"        ,  Giving  line  for 244,  270 

Tunnelling  trenches 272 

Typhoid-fever  germs  in  oysters 21 

Velocity  in  sewers,  Effect  of  depth  upon 69 

"        "       ,  Formula   for 61 

"       "      ,  Table  of 64 

"      ,  Maximum,   permissible 77 

"      ,  Minimum,  permissible  in  storm  and  combined  sewers....   74,76 

"     ,  "  house-sewers  71,  75 

"      ,  Uniform,  in  a  system 135 

Ventilation  of  sewers,  Methods  recommended  for 101,  344 

"        "      ,  Necessity   for 95,98 

"        "      ,  Various  expedients  for 98 

Vitrified  clay  pipe.     See  Pipe,  Vitrified. 

Walls,  Thickness  of  sewer 159,  165 

Water-carriage  system 7 

closet  tanks 344,  345 

"      closets,  Location  of 345 

Water  consumption  and  sewage  flow 31 

"  "          ,  Estimating  future 33,  114 

"  "  in  various  cities 32 

"    ,  ground,  Amount  of,  leaking  into  sewers 37,  169 


372  INDEX. 

PACK 

Water,  ground,  Detecting  presence  of no 

"      ,  Driven  wells  for  lowering 318 

"      ,  Handling  241,  310,  315,  318 

"  "      ,  Sub-drains  for  handling 312 

"       in  trenches,  Specifications  governing 199 

"    ,  Methods  of  constructing  sewers  under 329 

"     ,  Tamping  trenches  with 214 

Weston,  W.  Va.,  Gaugings  of  sewage  flow  at 40 

Wet  and  quicksand  trenches,  Pipe  joints  in 319 

"       ,  Size  of  gangs  for 268 

"       .  See  Water,  Ground. 

Winter,  Masonry  work  in 296,  308 

"      ,  Pipe-laying  in 308 

Wooden-stave  pipe 158 

Working  gangs,  Size  and  number  of 266 


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AGRICULTURE. 

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Arrnsby 's  Manual  of  Cattle  Feeding 12nio,  $1  75 

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1 


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Wait's  Engineering  and  Architectural  Jurisprudence 8vo,  6  00 

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World's  Columbian  Exposition  of  1893 Large  4to,  2  50 

ARMY,  NAVY,  Etc. 

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Hoff's  Naval  Tactics 8vo,  1  50 

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"        Handbook  of  Problems  in  Direct  Fire 8vo,  4  00 

2 


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"        Elements  of  the  Art  of  War 8vo,  4  00 

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Murray's  A  Manual  for  Courts-Martial 16mo,  morocco,  1  50 

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3 


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BRIDGES,  ROOFS,   Etc, 

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*  "      The  Thames  River  Bridge 4to,  paper,  5  00 

Burr's  Stresses  in  Bridges 8vo,  3  50 

Crehore's  Mechanics  of  the  Girder 8vo,  5  00 

Dredge's  Thames  Bridges 7  parts,  per  part,  1  25 

Du  Bois's  Stresses  in  Framed  Structures Small  4to,  10  00 

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Howe's  Treatise  on  Arches 8vo,  4  00 

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Wood's  Construction  of  Bridges  and  Roofs. Svo,  2  00 

Wright's  Designing  of  Draw  Spans.     Parts  I.  and  II.. Svo,  each  2  50 

"               "          "      "           "         Complete Svo,  350 


CHEMISTRY. 

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Adriance's  Laboratory  Calculations 12mo,  $1  25 

Allen's  Tables  for  Iron  Analysis 8vo,  3  00 

Austen's  Notes  for  Chemical  Students 12mo,  1  50 

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Crafts's  Qualitative  Analysis.     (Schaeffer.) 12mo,  1  50 

Drechsel's  Chemical  Reactions.    (Merrill.) 12mo,  1  25 

Fresenius's  Quantitative  Chemical  Analysis.    (Allen.) 8vo,  6  00 

Qualitative         "              "           (Johnson.) 8vo,  300 

(Wells.)         Trans. 

16th  German  Edition 8vo,  5  00 

Fuertes's  Water  and  Public  Health 12mo,  1  50 

Gill's  Gas  and  Fuel  Analysis 12mo,  1  25 

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Miller's  Chemical  Physics 8vo,  2  00 

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5 


Schimpfs  Volumetric  Analysis 12mo,  $2  50 

Spencer's  Sugar  Manufacturer's  Handbook 16mo,  morocco,  2  00 

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Machine  Construction 2  vols.,  8vo,  750 

Plane  Problems 12mo,  125 

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"        Projection  Drawing 12mo,  150 

6 


Warren's  Shades  and  Shadows 8vo,  $300 

' '        Stereotomy — Stone-cutting 8vo,  2  50 

Whelpley's  Letter  Engraving 12mo,  2  00 

ELECTRICITY  AND  MAGNETISM. 

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Anthony  and  Brackett's  Text-book  of  Physics.     (Magie.)   Small 

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Anthony's  Theory  of  Electrical  Measurements 12mo,  1  00 

Barker's  Deep-sea  Soundings 8vo,  2  00 

Benjamin's  Voltaic  Cell 8vo,  3  00 

History  of  Electricity 8vo,  300 

Classen's  Analysis  by  Electrolysis.    (Herrick  and  Boltwood.)  8vo,  3  00 

Cosmic  Law  of  Thermal  Repulsion 12nio,  75 

Crehore  and  Squier's  Experiments  with  a  New  Polarizing  Photo- 
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Dawson's  Electric  Railways  and  Tramways.     Small,  4to,  half 

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Vol.11 4to,  750 

Gilbert's  De  magnete.     (Mottelay.) 8vo,  2  50 

Holman's  Precision  of  Measurements 8vo,  2  00 

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Lob's  Electrolysis  and  Electrosynthesis  of  Organic  Compounds. 

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Morgan's  The  Theory  of  Solutions  and  its  Results 12mo,  1  00 

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Pratt  and  Aldeu's  Street-railway  Road-beds 8vo,  2  00 

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Thurston's  Stationary  Steam  Engines  for  Electric  Lighting  Pur- 
poses  8vo,  250 

*Tillman's  Heat 8vo,  1  50 

7 


ENGINEERING. 

CIVIL — MECHANICAL— SANITARY,  ETC. 

(See  also  BRIDGES,  p.  4 ;  HYDRAULICS,  p.  9 ;  MATERIALS  OF  EN- 
GINEERING, p.  10;  MECHANICS  AND  MACHINERY,  p.  12  ;  STEAM 
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Black's  U.  S.  Public  Works Oblong  4to,  5  00 

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Butts's  Civil  Engineers'  Field  Book 16mo,  morocco,  2  50 

Byrne's  Highway  Construction 8vo,  5  00 

"       Inspection  of  Materials  and  Workmanship 16mo,  3  00 

Carpenter's  Experimental  Engineering  .• 8vo,  6  00 

Church's  Mechanics  of  Engineering — Solids  and  Fluids. ..  .8vo,  6  00 

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Crandall's  Earthwork  Tables ; 8vo,  1  50 

' '          The  Transition  Curve 16mo,  morocco,  1  50 

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Gerhard's  Sanitary  House  Inspection 12mo,  1  00 

Godwin's  Railroad  Engineer's  Field-book 16mo,  morocco,  2  50 

Gore's  Elements  of  Geodesy Svo,  2  50 

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Howe's  Retaining  Walls  (New  Edition.) « 12mo,  1  25 

Hudson's  Excavation  Tables.     Vol.  II , 8vo,  1  00 

Button's  Mechanical  Engineering  of  Power  Plants Svo,  5  00 

Johnson's  Materials  of  Construction Large  Svo,  6  00 

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"         Theory  and  Practice  of  Surveying Small  8vo,  4  00 

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Mahan's  Civil  Engineering.     (Wood.) Svo,  5  00 

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Merriman's  Geodetic  Surveying Svo,  2  00 

Retaining  Walls  and  Masonry  Dams Svo,  2  00 

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Nagle's  Manual  for  Railroad  Engineers 16mo,  morocco,  3  00 

Ogden's  Sewer  Design.     (In  the  press.} 

Pattou's  Civil  Engineering Svo,  half  morocco,  7  50 

S 


Patton's  Foundations 8vo,  $5  00 

Pratt  and  Alden's  Street-railway  Road-beds 8vo,  2  00 

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Taylor's  Prismoidal  Formulas  and  Earthwork 8vo,  1  50 

Thurston's  Materials  of  Construction  8vo,  5  00 

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*  "           Cross-section Sheet,  25 

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*  "           Laying  Out  Curves 12mo,  morocco,  2  50 

Waddell's  De  Pontibus  (A  Pocket-book  for  Bridge  Engineers). 

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Wait's  Engineering  and  Architectural  Jurisprudence 8vo,  6  00 

Sheep,  6  50 

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New  Edition 1  25 

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Wellington's  Location  of  Railways Small  8vo,  5  00 

Wheeler's  Civil  Engineering 8vo,  4  00 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  00 


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Bazin's  Experiments  upon  the  Contraction  of  the  Liquid  Vein. 

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Herschel's  115  Experiments 8vo,  2  00 


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Weisbacb's  Hydraulics.     (Du  Bois.) 8vo,  5  00 

Wkipple's  Microscopy  of  Drinking  Water 8vo,  3  50 

Wilson 's  Irrigation  Engineering 8vo,  4  00 

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Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  00 

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MANUFACTURES. 

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Allen's  Tables  for  Iron  Analysis Svo,  3  00 

Beaumont's  Woollen  and  Worsted  Manufacture 12rno,  1  50 

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MATERIALS  OF  ENGINEERING. 

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